X86 Assembly Language Reference Manual

Home , Assembly language, Control register, Direction flag, HLT (x86 instruction), Instruction register, Interrupt flag

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Preface...... xvii 1. Assembler Input ...... 1 Introduction ...... 1 Source Files in Assembly Language Format...... 2 File Organization ...... 2 Statements...... 3 Values and Symbol Types ...... 4 Expressions...... 6 Expression Syntax ...... 7 Expression Semantics (Absolute vs. Relocatable) ...... 9 Machine Instruction Syntax ...... 10 Instruction Description ...... 12 Pseudo Operations ...... 14 General Pseudo Operations ...... 14 Symbol Deﬁnition Pseudo Operations ...... 19

iii 2. Instruction-Set Mapping ...... 21 Introduction ...... 22 Notational Conventions ...... 23 References ...... 26 Segment Register Instructions ...... 26 Load Full Pointer (lds,les, lfs, lgs, and lss) ...... 26 Pop Stack into Word (pop)...... 27 Push Word/Long onto Stack (push)...... 28 I/O Instructions ...... 29 Input from Port (in, ins) ...... 29 Output from Port (out, outs) ...... 31 Flag Instructions...... 32 Load Flags into AH Register (lahf) ...... 32 Store AH into Flags (sahf)...... 33 Pop Stack into Flag (popf) ...... 33 Push Flag Register Onto Stack (pushf) ...... 34 Complement Carry Flag (cmc)...... 35 Clear Carry Flag (clc)...... 35 Set Carry Flag (stc)...... 36 Clear Interrupt Flag (cli) ...... 36 Set Interrupt Flag (sti) ...... 37 Clear Direction Flag (cld) ...... 37 Set Direction Flag (std) ...... 38 Arithmetic Logical Instructions ...... 38

iv x86 Assembly Language Reference Manual—November 1995 Integer Addition (add) ...... 38 Integer Add With Carry (adc) ...... 39 Integer Subtraction (sub) ...... 40 Integer Subtraction With Borrow (sbb) ...... 41 Compare Two Operands (cmp) ...... 42 Increment by 1 (inc)...... 43 Decrease by 1 (dec) ...... 44 Logical Comparison or Test (test) ...... 45 Shift (sal, shl, sar, shr) ...... 46 Double Precision Shift Left (shld) ...... 48 Double Precision Shift Right (shrd)...... 49 One’s Complement Negation (not) ...... 50 Two’s Complement Negation (neg)...... 50 Check Array Index Against Bounds (bound)...... 51 Logical And (and) ...... 52 Logical Inclusive OR (or) ...... 54 Logical Exclusive OR (xor) ...... 55 Multiply and Divide Instructions ...... 56 Signed Multiply (imul) ...... 57 Unsigned Multiplication of AL, AX or EAX(mul) ...... 58 Unsigned Divide (div)...... 60 Signed Divide (idiv) ...... 61 Conversion Instructions ...... 62 Convert Byte to Word (cbtw) ...... 62

Contents v Convert Word to Long (cwtl) ...... 63 Convert Signed Word to Signed Double Word (cwtd) . . . . 63 Convert Signed Long to Signed Double Long (cltd) ...... 64 Decimal Arithmetic Instructions ...... 64 Decimal Adjust AL after Addition (daa) ...... 64 Decimal Adjust AL after Subtraction (das)...... 65 ASCII Adjust after Addition (aaa) ...... 65 ASCII Adjust after Subtraction (aas) ...... 66 ASCII Adjust AX after Multiply (aam) ...... 67 ASCII Adjust AX before Division (aad) ...... 68 Coprocessor Instructions...... 69 Wait (wait, fwait) ...... 69 String Instructions ...... 69 Move Data from String to String (movs)...... 70 Compare String Operands (cmps) ...... 71 Store String Data (stos) ...... 72 The Load String Operand (lods) ...... 73 Compare String Data (scas) ...... 75 Look-Up Translation Table (xlat) ...... 76 Repeat String Operation (rep, repnz, repz) ...... 77 Procedure Call and Return Instructions ...... 78 Far Call — Procedure Call (lcall) ...... 78 Near Call — Procedure Call (call) ...... 79 Return from Procedure (ret) ...... 80

vi x86 Assembly Language Reference Manual—November 1995 Long Return (lret) ...... 81 Enter/Make Stack Frame for Procedure Parameters (enter) 82 High Level Procedure Exit (leave)...... 83 Jump Instructions...... 83 Jump if ECX is Zero (jcxz)...... 83 Loop Control with CX Counter (loop, loopnz, loopz). . . . . 84 Jump (jmp, ljmp) ...... 85 Interrupt Instructions ...... 87 Call to Interrupt Procedure (int, into) ...... 87 Interrupt Return (iret) ...... 89 Protection Model Instructions ...... 90 Store Local Descriptor Table Register (sldt) ...... 90 Store Task Register (str)...... 90 Load Local Descriptor Table Register (lldt) ...... 91 Load Task Register (ltr)...... 92 Verify a Segment for Reading or Writing (verr, verw) . . . . 92 Store Global/Interrupt Descriptor Table Register (sgdt, sidt) 93 Load Global/Interrupt Descriptor Table (lgdt, lidt) ...... 94 Store Machine Status Word (smsw)...... 95 Load Machine Status Word (lmsw) ...... 96 Load Access Rights (lar) ...... 96 Load Segment Limit (lsl)...... 97 Clear Task-Switched (clts)...... 98 Adjust RPL Field of Selector (arpl) ...... 99

Contents vii Bit Instructions ...... 100 Bit Scan Forward (bsf) ...... 100 Bit Scan Reverse (bsr) ...... 100 Bit Test (bt) ...... 101 Bit Test And Complement (btc) ...... 102 Bit Test And Reset (btr) ...... 102 Bit Test And Set (bts) ...... 103 Exchange Instructions ...... 103 Compare and Exchange (cmpxchg)[486] ...... 103 Floating-Point Transcendental Instructions ...... 104 Floating-Point Sine (fsin) ...... 104 Floating-Point Cosine (fcos) ...... 104 Floating-Point Sine and Cosine (fsincos) ...... 104 Floating-Point Constant Instructions...... 105 Floating-Point Load One (fld) ...... 105 Processor Control Floating-Point Instructions ...... 105 Floating-Point Load Control Word (fldcw)...... 105 Floating-Point Load Environment (fldenv) ...... 106 Miscellaneous Floating-Point Instructions ...... 106 Floating-Point Different Reminder (fprem) ...... 106 Floating-Point Comparison Instructions...... 106 Floating-Point Unsigned Compare (fucom) ...... 106 Floating-Point Unsigned Compare And Pop (fucomp) . . . 107 Floating-Point Unsigned Compare And Pop Two (fucompp)107

viii x86 Assembly Language Reference Manual—November 1995 Load and Move Instructions...... 108 Load Effective Address (lea)...... 108 Move (mov) ...... 109 Move Segment Registers (movw) ...... 109 Move Control Registers (mov) ...... 110 Move Debug Registers (mov)...... 111 Move Test Registers (mov) ...... 111 Move With Sign Extend (movsx) ...... 112 Move With Zero Extend (movzb) ...... 112 Pop Instructions ...... 113 Pop All General Registers (popa) ...... 113 Push Instructions ...... 114 Push All General Registers (pusha)...... 114 Rotate Instructions...... 114 Rotate With Carry Left (rcl) ...... 114 Rotate With Carry Right (rcr) ...... 115 Rotate Left (rol) ...... 116 Rotate Right (ror) ...... 117 Byte Instructions ...... 118 Byte Set On Condition (setcc)...... 118 Byte Swap (bswap) [486]...... 120 Exchange Instructions ...... 120 Exchange And Add (xadd) [486] ...... 120 Exchange Register / Memory With Register (xchg) ...... 120

Contents ix Miscellaneous Instructions ...... 121 Write Back and Invalidate Cache (wbinvd) [486 only] . . . . 121 Invalidate (invd) [486 only] ...... 122 Invalidate Page (invlpg) [486 only] ...... 122 LOCK Prefix (lock)...... 122 No Operation (nop) ...... 123 Halt (hlt) ...... 124 Real Transfer Instructions ...... 125 Load Real (fld) ...... 125 Store Real (fst) ...... 125 Store Real and Pop (fstp) ...... 126 Exchange Registers (fxch) ...... 126 Integer Transfer Instructions ...... 127 Integer Load (fild) ...... 127 Integer Store (fist) ...... 127 Integer Store and Pop (fistp)...... 127 Packed Decimal Transfer Instructions...... 128 Packed Decimal (BCD) Load (fbld) ...... 128 Packed Decimal (BCD) Store and Pop (fbstp) ...... 128 Addition Instructions ...... 129 Real Add (fadd) ...... 129 Real Add and Pop (faddp) ...... 129 Integer Add (fiadd) ...... 129 Subtraction Instructions ...... 130

x x86 Assembly Language Reference Manual—November 1995 Subtract Real and Pop (fsub) ...... 130 Subtract Real (fsubp) ...... 130 Subtract Real Reversed (fsubr)...... 130 Subtract Real Reversed and Pop (fsubrp) ...... 131 Integer Subtract (fisubrp) ...... 131 Integer Subtract Reverse (fisubr) ...... 131 Multiplication Instructions ...... 132 Multiply Real (fmul) ...... 132 Multiply Real and Pop (fmulp) ...... 132 Integer Multiply (fimul) ...... 132 Division Instructions ...... 133 Divide Real (fdiv)...... 133 Divide Real and Pop (fdivp)...... 133 Divide Real Reversed (fdivr) ...... 133 Divide Real Reversed and Pop (fdivrp) ...... 134 Integer Divide (fidiv)...... 134 Integer Divide Reversed (fidivr) ...... 134 Miscellaneous Arithmetic Operations...... 136 Square Root (fsqrt)...... 136 Scale (fscale) ...... 136 Partial Remainder (fprem) ...... 136 Round to Integer (frndint) ...... 137 Extract Exponent and Significand (fxtract)...... 137 Absolute Value (fabs) ...... 137

Contents xi Change Sign (fchs) ...... 138 Comparison Instructions...... 138 Compare Real (fcom)...... 138 Compare Real and Pop (fcomp)...... 139 Compare Real and Pop Twice (fcompp) ...... 139 Integer Compare (ﬁcom)...... 139 Integer Compare and Pop (ﬁcomp) ...... 140 Test (ftst) ...... 140 Examine (fxam) ...... 140 Transcendental Instructions ...... 141 Partial Tangent (fptan) ...... 141 Partial Arctangent (fpatan)...... 142 2x - 1 (f2xm1) ...... 142 Y * log2 X (fyl2x) ...... 142 Y * log2 (X+1) (fyl2xp1) ...... 143 Constant Instructions ...... 143

Load log2 E (ﬂdl2e) ...... 143

Load log2 10 (ﬂdl2t) ...... 143

Load log10 2 (ﬂdlg2)...... 144

Load loge 2 (fldln2) ...... 144 Load pi (fldpi) ...... 144 Load + 0 (fldz) ...... 145 Processor Control Instructions ...... 145 Initialize Processor (finit, fnint) ...... 145

xii x86 Assembly Language Reference Manual—November 1995 No Operation (fnop) ...... 145 Save State (fsave, fnsave) ...... 146 Store Control Word (fstcw, fnstcw) ...... 146 Store Environment (fstenv, fnstenv) ...... 146 Store Status Word (fstsw, fnstsw)...... 147 Restore State (frstor) ...... 147 CPU Wait (fwait, wait) ...... 147 Clear Exceptions (fclex, fnclex) ...... 148 Decrement Stack Pointer (fdecstp)...... 148 Free Registers (ffree) ...... 148 Increment Stack Pointer (ﬁncstp)...... 149 3. Assembler Output...... 151 Introduction ...... 151 Object Files in Executable and Linking Format (ELF) ...... 152 ELF Header...... 153 Section Header ...... 155 Sections ...... 159 Symbol Tables...... 162 String Tables ...... 164 A. Using the Assembler Command Line ...... 167 Assembler Command Line ...... 167 Assembler Command Line Options ...... 168 Disassembling Object Code ...... 169 Index ...... 171

Contents xiii xiv x86 Assembly Language Reference Manual—November 1995 Tables

Table 1-1 Object File Sections ...... 6 Table 1-2 Operators Supported by the Assembler...... 6 Table 1-3 Syntactical Rules of Expressions ...... 8 Table 1-4 8-bit (byte) General Registers...... 11 Table 1-5 16-bit (word) General Registers...... 11 Table 1-6 32-bit (long ) General Registers ...... 12 Table 1-7 Description of Segment Registers ...... 12 Table 2-1 Condition Codes ...... 25 Table 2-2 Logical AND...... 53 Table 2-3 Inclusive OR ...... 54 Table 2-4 Exclusive XOR ...... 56 Table 2-5 Clearing OF and CF flags — imul...... 57 Table 2-6 Clearing OF and CF flags — mul ...... 59 Table 2-7 idiv Register Assignment ...... 62 Table 2-8 Handling a Carry...... 66 Table 2-9 How aas Handles a Carry...... 67

xv Table 2-10 setcc Condition List ...... 119 Table 2-11 Floating-point Opcodes ...... 135 Table 3-1 Object File Types ...... 155

Table 3-2 Section Attribute Flags ...... 157 Table 3-3 Section Types ...... 157 Table 3-4 Predefined User Sections ...... 161 Table 3-5 Predefined Non-User Sections...... 161 Table 3-6 Symbol Types...... 164 Table 3-7 Symbol Bindings ...... 164

xvi x86 Assembly Language Reference Manual—November 1995 Preface

This preface is a brief description of the SunOS™ assembler that runs on x86. This preface also includes a list of documents that can be used for reference.

The SunOS assembler that runs on x86, referred to as the “SunOS x86” in this manual, translates source ﬁles that are in assembly language format into object ﬁles in linking format.

In the program development process, the assembler is a tool to use in producing program modules intended to exploit features of the Intel® architecture in ways that cannot be easily done using high level languages and their compilers.

Whether assembly language is chosen for the development of program modules depends on the extent to which and the ease with which the language allows the programmer to control the architectural features of the processor.

The assembly language described in this manual offers full direct access to the x86 instruction set. The assembler may also be used in connection with SunOS 5.1 macro preprocessors to achieve full macro-assembler capability. Furthermore, the assembler responds to directives that allow the programmer direct control over the contents of the relocatable object ﬁle.

This document describes the language in which the source ﬁles must be written. The nature of the machine mnemonics governs the way in which the program’s executable portion is written. This document includes descriptions of the pseudo operations that allow control over the object ﬁle. This facilitates the development of programs that are easy to understand and maintain.

xvii Before You Read This Book

Use the following documents as references: • Intel 80386 Programmer’s Reference Manual • i486™ Microprocessor Programmer Reference Manual (1990) • Intel 80387 Programmer’s Reference Manual (1987) • System V Application Binary Interface Intel 386 Processor Supplement • System V Application Binary Interface • SVID System V Interface Deﬁnition

You should also become familiar with the following: • Man pages: as(1), ld(1), cpp(1), mn(4),cof2elf(1) (elf - Executable and Linking Format), elf(3E), dis(1), a.out(5). • ELF-related sections of the Programming Utilities manual.

How This Book Is Organized

This document is organized into the following chapters:

Chapter 1, “Assembler Input,” describes the overall structure required by the assembler for input source ﬁles.

Chapter 2, “Instruction-Set Mapping,” describes the instruction set mappings for the SunOS x86 processor.

Chapter 3, “Assembler Output,” provides an overview of ELF (Executable and Linking Format) for the relocatable object ﬁles produced by the assembler.

Appendix A, “Using the Assembler Command Line,” describes the assembler command line options.

xviii x86 Assembly Language Reference Manual—November 1995 What Typographic Changes Mean

The following table describes the typographic changes used in this book.

Table P-1 Typographic Conventions

Typeface or Symbol Meaning Example AaBbCc123 The names of commands, Edit your .login file. files, and directories; Use ls -a to list all files. on-screen computer output machine_name% You have mail.

AaBbCc123 What you type, contrasted machine_name% su with on-screen computer Password: output AaBbCc123 Command-line placeholder: To delete a ﬁle, type rm ﬁlename. replace with a real name or value AaBbCc123 Book titles, new words or Read Chapter 6 in User’s Guide. terms, or words to be These are called class options. emphasized You must be root to do this.

Shell Prompts in Command Examples

The following table shows the default system prompt and superuser prompt for the C shell, Bourne shell, and Korn shell.

Table P-2 Shell Prompts

Shell Prompt C shell prompt machine_name% C shell superuser prompt machine_name# Bourne shell and Korn shell $ prompt Bourne shell and Korn shell # superuser prompt

Preface xix xx x86 Assembly Language Reference Manual—November 1995 Assembler Input 1

The SunOS x86 assembler translates source files in the assembly language format specified in this document into relocatable object files for processing by the link editor. This translation process is called assembly. The main input required to assemble a source file in assembly language format is that source file itself.

This chapter has the following organization:

Introduction page 1 Source Files in Assembly Language Format page 2 Pseudo Operations page 14

Introduction

In whatever manner it is produced, the source input file must have a certain structure and content. The specification of this structure and content constitutes the syntax of the assembly language. A source file may be produced by one of the following: • A programmer using a text editor • A compiler as an intermediate step in the process of translating from a high- level language to executable code • An automatic program generator • Some other mechanism.

1 1

The assembler may also allow ancillary input incidental to the translation process. For example, there are several invocation options available. Each such option exercised constitutes information input to the assembler. However, this ancillary input has little direct connection to the translation process, so it is not properly a subject for this manual. Information about invoking the assembler and the available options appears in the as(1) man pages.

This chapter describes the overall structure required by the assembler for input source files. This structure is relatively simple: the input source file must be a sequence of assembly language statements. This chapter also begins the specification of the contents of the input source file by describing assembly language statements as textual objects of a certain form.

This document completes the speciﬁcation by presenting detailed assembly language statements that correspond to the Intel instruction set and are intended for use on machines that run SunOS x86 architecture. For more information on assembly language instruction sets, please refer to the product documentation from Intel Corporation.

Source Files in Assembly Language Format

This section details the following: • ﬁle organization • statements • values and symbols • expressions • machine instruction syntax

File Organization

Input to the assembler is a text ﬁle consisting of a sequence of statements. Each statement ends with the ﬁrst occurrence of a newline character (ASCII LF), or of a semicolon (;) that is not within a string operand or between a slash and a newline character. Thus, it is possible to have several statements on one line.

2 x86 Assembly Language Reference Manual—November 1995 1

To make programs easy to read, understand and maintain, however, it is good programming practice not to have more than one statement per line. As indicated above, a line may contain one or more statements. If several statements appear on a line, they must be separated by semicolons (;).

Statements

This section outlines the types of statements that apply to assembly language. Each statement must be one of the following types: • An empty statement is one that contains nothing other than spaces, tabs, or formfeed characters.

Empty statements have no meaning to the assembler. They can be inserted freely to improve the appearance of a source ﬁle or of a listing generated from it. • An assignment statement is one that gives a value to a symbol. It consists of a symbol, followed by an equal sign (=), followed by an expression.

The expression is evaluated and the result is assigned to the symbol. Assignment statements do not generate any code. They are used only to assign assembly time values to symbols. • A pseudo operation statement is a directive to the assembler that does not necessarily generate any code. It consists of a pseudo operation code, optionally followed by operands. Every pseudo operation code begins with a period (.). • A machine operation statement is a mnemonic representation of an executable machine language instruction to which it is translated by the assembler. It consists of an operation code, optionally followed by operands.

Furthermore, any statement remains a statement even if it is modiﬁed in either or both of the following ways: • Preﬁxing a label at the beginning of the statement.

A label consists of a symbol followed by a colon (:). When the assembler encounters a label, it assigns the value of the location counter to the label. • Appending a comment at the end of the statement by preceding the comment with a slash (/).

Assembler Input 3 1

The assembler ignores all characters following a slash up to the next occurrence of newline. This facility allows insertion of internal program documentation into the source ﬁle for a program.

Values and Symbol Types

This section presents the values and symbol types that the assembler uses.

Values

Values are represented in the assembler by numerals which can be faithfully represented in standard two’s complement binary positional notation using 32 bits. All integer arithmetic is performed using 32 bits of precision. Note, however, that the values used in an x86 instruction may require 8, 16, or 32 bits.

Symbols

A symbol has a value and a symbol type, each of which is either speciﬁed explicitly by an assignment statement or implicitly from context. Refer to the next section for the regular deﬁnition of the expressions of a symbol.

The following symbols are reserved by the assembler:

.Commonly referred to as dot. This is the location counter while assembling a program. It takes on the current location in the text, data, or bss section.

.text This symbol is of type text. It is used to label the beginning of a .text section in the program being assembled.

.data This symbol is of type data. It is used to label the beginning of a data section in the program being assembled.

.bss This symbol is of type bss. It is used to label the beginning of a .bss section in the program being assembled.

4 x86 Assembly Language Reference Manual—November 1995 1

.init This is used with C++ programs which require constructors.

.fini This is used with C++ programs which require destructors.

Symbol Types

Symbol type is one of the following: undefined A value is of undefined symbol type if it has not yet been defined. Example instances of undefined symbol types are forward references and externals. absolute A value is of absolute symbol type it does not change with relocation. Example instances of absolute symbol types are numeric constants and expressions whose proper sub-expressions are themselves all absolute. text A value is of text symbol type if it is relative to the .text section. data A value is of data symbol type if it is relative to the .data section. bss A value is of bss symbol type if it is relative to the .bss section.

You can give any of these symbol types the attribute EXTERNAL.

Sections

Five of the symbol types are defined with respect to certain sections of the object file into which the assembler translates the source file. This section describes symbol types.

Assembler Input 5 1

If the assembler translates a particular assembly language statement into a machine language instruction or into a data allocation, the translation is associated with one of the following five sections of the object file into which the assembler is translating the source file: Table 1-1 Object File Sections

Section Purpose

text This is an initialized section. Normally, it is read-only and contains code from a program. It may also contain read-only tables

data This is an initialized section. Normally, it is readable and writable. It contains initialized data. These can be scalars or tables.

bss This is an initialized section. Space is not allocated for this segment in the object ﬁle.

init This is used with C++ programs that require constructors.

fini This is used by C++ programs that require destructors.

An optional section, .comment, may also be produced (see Chapter 3, “Assembler Output”).

The section associated with the translated statement is .text unless the original statement occurs after a section control pseudo operation has directed the assembler to associate the statement with another section.

Expressions

The expressions accepted by the x86 assembler are deﬁned by their syntax and semantics. The following are the operators supported by the assembler:

Table 1-2 Operators Supported by the Assembler

Operator Action + Addition - Subtraction \* Multiplication \/ Division

6 x86 Assembly Language Reference Manual—November 1995 1

Table 1-2 Operators Supported by the Assembler

Operator Action & Bitwise logical and | Bitwise logical or >> Right shift << Left shift \% Remainder operator ! Bitwise logical and not

Expression Syntax

Table 1-3 shows syntactic rules, the non terminals are represented by lowercase letters, the terminal symbols are represented by uppercase letters, and the symbols enclosed in double quotes are terminal symbols. There is no precedence assigned to the operators. You must use square brackets to establish precedence.

Assembler Input 7 1

Table 1-3 Syntactical Rules of Expressions

~~id : LABEL ;~~

~~number : DEC_VAL | HEX_VAL | OCT_VAL | BIN_VAL ;~~

~~The terminal nodes are given by the following regular expressions:~~

LABEL = [a-zA-Z_][a-zA-Z0-9_]*: DEC_VAL = [1-9][0-9]* HEX_VAL = 0[Xx][0-9a-fA-F][0-9a-fA-F]* OCT_VAL = 0[0-7]* BIN_VAL = 0[Bb][0-1][0-1]*

~~8 x86 Assembly Language Reference Manual—November 1995 1~~

In the above regular expressions, choices are enclosed in square brackets; a range of choices is indicated by letters or numbers separated by a dash (-); and the asterisk (*) indicates zero or more instances of the previous character.

~~Expression Semantics (Absolute vs. Relocatable)~~

Semantically, the expressions fall into two groups, absolute and relocatable. The equations later in this section show the legal combinations of absolute and relocatable operands for the addition and subtraction operators. All other operations are only legal on absolute-valued expressions.

All numbers have the absolute attribute. Symbols used to reference storage, text, or data are relocatable. In an assignment statement, symbols on the left side inherit their relocation attributes from the right side.

~~In the equations below, a is an absolute-valued expression and r is a relocatable-valued expression. The resulting type of the operation is shown to the right of the equal sign.~~

~~a + a = a r + a = r a - a = a r - a = r r - r = a~~

~~In the last example, you must declare the relocatable expressions before taking their difference.~~

~~Following are some examples of valid expressions:~~

~~label $label [label + 0x100] [label1 - label2] $[label1 - label2]~~

~~Assembler Input 9 1~~

~~Following are some examples of invalid expressions:~~

~~[$label - $label] [label1 * 5] (label + 0x20)~~

~~Machine Instruction Syntax~~

This section describes the instructions that the assembler accepts. The detailed speciﬁcation of how the particular instructions operate is not included; for this, see Intel’s 80386 Programmer’s Reference Manual.

The following list describes the three main aspects of the SunOS x86 assembler: • All register names use the percent sign (%) as a prefix to distinguish them from symbol names. • Instructions with two operands use the left one as the source and the right one as the destination. This follows the SunOS operating environment assembler convention, and is reversed from Intel’s notation. • Most instructions that can operate on a byte, word, or long may have b, w, or l appended to them. When an opcode is specified with no type suffix, it usually defaults to long. In general, the SunOS assembler derives its type information from the opcode, where the Intel assembler can derive its type information from the operand types. Where the type information is derived motivates the b, w, and l suffixes used in the SunOS assembler. For example, in the instruction movw $1,%eax the w suffix indicates the operand is a word.

~~Operands~~

Three kinds of operands are generally available to the instructions: register, memory, and immediate. Full descriptions of each type appear in “Notational Conventions” on page 23. Indirect operands are available only to jump and call instructions.

~~The assembler always assumes it is generating code for a 32-bit segment. When 16-bit data is called for (e.g., movw %ax, %bx), the assembler automatically generates the 16-bit data preﬁx byte.~~

~~10 x86 Assembly Language Reference Manual—November 1995 1~~

Byte, word, and long registers are available on the x86 processor. The instruction pointer (%eip) and ﬂag register (%efl) are not available as explicit operands to the instructions. The code segment (%cs) may be used as a source operand but not as a destination operand.

~~The names of the byte, word, and long registers available as operands and a brief description of each follow. The segment registers are also listed.~~

~~Table 1-4 8-bit (byte) General Registers~~

%al Low byte of %ax register %ah High byte of %ax register %cl Low byte of %cx register %ch High byte of %cx register %dl Low byte of %dx register %dh High byte of %dx register %bl Low byte of %bx register %bh High byte of %bx register

~~Table 1-5 16-bit (word) General Registers~~

%ax Low 16-bits of %eax register %cx Low 16-bits of %ecx register %dx Low 16-bits of %edx register %bx Low 16-bits of %ebx register %sp Low 16-bits of the stack pointer %bp Low 16-bits of the frame pointer %si Low 16-bits of the source index register %di Low 16-bits of the destination index register

~~Assembler Input 11 1~~

~~Table 1-6 32-bit (long ) General Registers~~

%eax 32-bit general register %ecx 32-bit general register %edx 32-bit general register %ebx 32-bit general register %esp 32-bit stack pointer %ebp 32-bit frame pointer %esi 32-bit source index register %edi 32-bit destination index register

~~Table 1-7 Description of Segment Registers~~

%cs Code segment register; all references to the instruction space use this register %ds Data segment register, the default segment register for most references to memory operands %ss Stack segment register, the default segment register for memory operands in the stack (i.e., default segment register for %bp, %sp, %esp, and %ebp) %es General-purpose segment register; some string instructions use this extra segment as their default segment %fs General-purpose segment register %gs General-purpose segment register

~~Instruction Description~~

~~This section describes the SunOS x86 instruction syntax.~~

~~The assembler assumes it is generating code for a 32-bit segment, therefore, it also assumes a 32-bit address and automatically precedes word operations with a 16-bit data preﬁx byte.~~

~~12 x86 Assembly Language Reference Manual—November 1995 1~~

~~Addressing Modes~~

~~Addressing modes are represented by the following:~~

~~[sreg:][offset][([base][,index][,scale])]~~

• All the items in the square brackets are optional, but at least one is necessary. If you use any of the items inside the parentheses, the parentheses are mandatory. • sreg is a segment register override prefix. It may be any segment register. If a segment override prefix is present, you must follow it by a colon before the offset component of the address. sreg does not represent an address by itself. An address must contain an offset component. • offset is a displacement from a segment base. It may be absolute or relocatable. A label is an example of a relocatable offset. A number is an example of an absolute offset. • base and index can be any 32-bit register. scale is a multiplication factor for the index register field. Its value may be 1, 2, 4, 8 to indicate the number to multiply by. The multiplication then occurs by 1, 2, 4, and 8.

~~Refer to Intel’s 80386 Programmer’s Reference Manual for more details on x86 addressing modes.~~

Following are some examples of addresses: movl var, %eax Move the contents of memory location var into %eax. movl %cs:var, %eax Move the contents of the memory location var in the code segment into %eax. movl $var, %eax Move the address of var into %eax. movl array_base(%esi), %eax Add the address of memory location array_base to the contents of %esi to get an address in memory. Move the contents of this address into %eax.

~~Assembler Input 13 1~~

~~movl (%ebx, %esi, 4), %eax Multiply the contents of %esi by 4 and add this to the contents of %ebx to produce a memory reference. Move the contents of this memory location into %eax.~~

movl struct_base(%ebx, %esi, 4), %eax Multiply the contents of %esi by 4, add this to the contents of %ebx, and add this to the address of struct_base to produce an address. Move the contents of this address into %eax.

~~Expressions and Immediate Values~~

~~An immediate value is an expression preceded by a dollar sign:~~

immediate: "$" expr Immediate values carry the absolute or relocatable attributes of their expression component. Immediate values cannot be used in an expression, and should be considered as another form of address, i.e., the immediate form of address.

~~immediate: "$" expr "," "$" expr The ﬁrst expr is 16 bits of segment. The second expr is 32 bits of offset.~~

~~Pseudo Operations~~

~~The pseudo-operations listed in this section are supported by the x86 assembler.~~

~~General Pseudo Operations~~

~~Below is a list of the pseudo operations supported by the assembler. This is followed by a separate listing of pseudo operations included for the beneﬁt of the debuggers (dbx(1)).~~

~~.align val The align pseudo op causes the next data generated to be aligned modulo val. val should be a positive integer value.~~

~~14 x86 Assembly Language Reference Manual—November 1995 1~~

~~.bcd val The.bcd pseudo op generates a packed decimal (80-bit) value into the current section. This is not valid for the.bss section. val is a nonﬂoating- point constant.~~

~~.bss The.bss pseudo op changes the current section to.bss.~~

~~.bss tag, bytes Deﬁne symbol tag in the.bss section and add bytes to the value of dot for.bss. This does not change the current section to.bss. bytes must be a positive integer value.~~

~~.byte val [, val] The.byte pseudo op generates initialized bytes into the current section. This is not valid for.bss. Each val must be an 8-bit value.~~

.comm name, expr [, alignment] The.comm pseudo op allocates storage in the .data section. The storage is referenced by the symbol name, and has a size in bytes of expr. expr must be a positive integer. name cannot be predeﬁned. If the alignment is given, the address of the name is aligned to a multiple of alignments.

~~.data The data pseudo op changes the current section to .data.~~

.double val The .double pseudo op generates an 80387 64 bit ﬂoating-point constant (IEEE 754) into the current section. Not valid in the .bss section. val is a ﬂoating-point constant. val is a string acceptable to atof(3); that is, an optional sign followed by a non-empty string of digits with optional decimal point and optional exponent.

~~.even The .even pseudo op aligns the current program counter (.) to an even boundary.~~

~~Assembler Input 15 1~~

.file "string" The .file op creates a symbol table entry where string is the symbol name and STT_FILE is the symbol table type. string specifies the name of the source file associated with the object file.

.float val The .float pseudo op generates an 80387 32 bit ﬂoating-point constant (IEEE 754) into the current section. This is not valid in the .bss section. val is a ﬂoating-point constant. val is a string acceptable to atof(3); that is, an optional sign followed by a non-empty string of digits with optional decimal point and optional exponent.

.globl symbol [, symbol]* The globl op declares each symbol in the list to be global; that is, each symbol is either defined externally or defined in the input file and accessible in other files; default bindings for the symbol are overridden.

• A global symbol definition in one file satisfies an undefined reference to the same global symbol in another file. • Multiple definitions of a defined global symbol is not allowed. If a defined global symbol has more than one definition, an error occurs.

~~Note – This pseudo-op by itself does not deﬁne the symbol.~~

~~.ident “string” The .ident pseudo op creates an entry in the comment section containing string. string is any sequence of characters, not including the double quote (").~~

.lcomm name, expr The .lcomm pseudo op allocates storage in the .bss section. The storage is referenced by the symbol name, and has a size of expr. name cannot be predeﬁned, and expr must be a positive integer type. If the alignment is given, the address of name is aligned to a multiple of alignment.

~~16 x86 Assembly Language Reference Manual—November 1995 1~~

.local symbol [, symbol]* Declares each symbol in the list to be local; that is, each symbol is defined in the input file and not accessible in other files; default bindings for the symbol are overridden. These symbols take precedence over weak and global symbols.

~~Because local symbols are not accessible to other ﬁles, local symbols of the same name may exist in multiple ﬁles.~~

~~Note – This pseudo-op by itself does not deﬁne the symbol.~~

.long val The .long pseudo op generates a long integer (32-bit, two’s complement value) into the current section. This pseudo op is not valid for the .bss section. val is a nonﬂoating-point constant.

~~.nonvolatile Deﬁnes the end of a block of instruction. The instructions in the block may not be permuted. This pseudo-op has no effect if:~~

~~• The block of instruction has been previously terminated by a Control Transfer Instruction (CTI) or a label • There is no preceding .volatile pseudo-op~~

~~.section section_name [, attributes]~~

~~Makes the speciﬁed section the current section.~~

The assembler maintains a section stack which is manipulated by the section control directives. The current section is the section that is currently on top of the stack. This pseudo-op changes the top of the section stack. • If section_name does not exist, a new section with the specified name and attributes is created. • If section_name is a non-reserved section, attributes must be included the first time it is specified by the .section directive.

~~.set name, expr The .set pseudo op sets the value of symbol name to expr. This is equivalent to an assignment.~~

~~Assembler Input 17 1~~

.string “str” This pseudo op places the characters in str into the object module at the current location and terminates the string with a null. The string must be enclosed in double quotes (""). This pseudo op is not valid for the .bss section.

~~.text The .text pseudo op deﬁnes the current section as .text.~~

.value expr [,expr] The .value pseudo op is used to generate an initialized word (16-bit, two’s complement value) into the current section. This pseudo op is not valid in the .bss section. Each expr must be a 16-bit value.

~~.version string The .version pseudo op puts the C compiler version number into the .comment section.~~

.volatile Deﬁnes the beginning of a block of instruction. The instructions in the section may not be changed. The block of instruction should end at a .nonvolatile pseudo-op and should not contain any Control Transfer Instructions (CTI) or labels. The volatile block of instructions is terminated after the last instruction preceding a CTI or label.

.weak symbol [, symbol] Declares each symbol in the list to be defined either externally, or in the input file and accessible to other files; default bindings of the symbol are overridden by this directive.

• A weak symbol definition in one file satisfies an undefined reference to a global symbol of the same name in another file. • Unresolved weak symbols have a default value of zero; the link editor does not resolve these symbols. • If a weak symbol has the same name as a defined global symbol, the weak symbol is ignored and no error results.

~~Note – This pseudo-op does not itself deﬁne the symbol.~~

~~18 x86 Assembly Language Reference Manual—November 1995 1~~

~~symbol =expr Assigns the value of expr to symbol.~~

~~Symbol Deﬁnition Pseudo Operations~~

~~.def name The .def pseudo op starts a symbolic description for symbol name. See endef. name is a symbol name.~~

.dim expr [,expr] The .dim pseudo op is used with the .def pseudo op. If the name of a .def is an array, the expressions give the dimensions; up to four dimensions are accepted. The type of each expression should be positive.

~~.endef The .endef pseudo op is the ending bracket for a .def.~~

~~.file name The .file pseudo op is the source file name. Only one is allowed per source file. This must be the first line in an assembly file.~~

~~.line expr The .line pseudo op is used with the .def pseudo op. It deﬁnes the source line number of the deﬁnition of symbol name in the .def. expr should yield a positive value.~~

~~.ln line [,addr] This pseudo op provides the relative source line number to the beginning of a function. It is used to pass information through to sdb.~~

~~.scl expr The .scl pseudo op is used with the .def pseudo op. Within the .def it gives name the storage class of expr. The type of expr should be positive.~~

~~Assembler Input 19 1~~

~~.size expr The .size pseudo op is used with the .def pseudo op. If the name of a .def is an object such as a structure or an array, this gives it a total size of expr. expr must be a positive integer.~~

.stabs name type 0 desc value .stabn type 0 desc value The .stabs and .stabn pseudo ops are debugger directives generated by the C compiler when the -g option are used. name provides the symbol table name and type structure. type identifies the type of symbolic information (i.e., source file, global symbol, or source line). desc specifies the number of bytes occupied by a variable or type, or the nesting level for a scope symbol. value specifies an address or an offset.

.tag str The .tag pseudo op is used in conjunction with a previously deﬁned .def pseudo op. If the name of a .def is a structure or a union, str should be the name of that structure or union tag deﬁned in a previous .def-.endef pair.

~~.type expr The .type pseudo op is used within a .def-.endef pair. It gives name the C compiler type representation expr.~~

~~.val expr The .val pseudo op is used with a .def-.endef pair. It gives name (in the .def) the value of expr. The type of expr determines the section for name.~~

~~20 x86 Assembly Language Reference Manual—November 1995 Instruction-Set Mapping 2~~

This chapter describes the instruction set mappings for the SunOS x86 processor. For more details of the operation and a summary of the exceptions, please refer to the i486 Microprocessor Programmer’s Reference Manual from Intel Corporation.

~~This chapter is organized as follows:~~

Introduction page 22 Segment Register Instructions page 26 I/O Instructions page 29 Flag Instructions page 32 Arithmetic Logical Instructions page 38 Multiply and Divide Instructions page 56 Conversion Instructions page 62 Decimal Arithmetic Instructions page 64 Coprocessor Instructions page 69 String Instructions page 69 Procedure Call and Return Instructions page 78 Jump Instructions page 83 Interrupt Instructions page 87 Protection Model Instructions page 90 Bit Instructions page 100 Exchange Instructions page 103

~~21 2~~

Floating-Point Transcendental Instructions page 104 Floating-Point Constant Instructions page 105 Processor Control Floating-Point Instructions page 105 Miscellaneous Floating-Point Instructions page 106 Floating-Point Comparison Instructions page 106 Load and Move Instructions page 108 Pop Instructions page 113 Push Instructions page 114 Rotate Instructions page 114 Byte Instructions page 118 Exchange Instructions page 120 Miscellaneous Instructions page 121 Real Transfer Instructions page 125 Integer Transfer Instructions page 127 Packed Decimal Transfer Instructions page 128 Addition Instructions page 129 Subtraction Instructions page 130 Multiplication Instructions page 132 Division Instructions page 133 Miscellaneous Arithmetic Operations page 136 Comparison Instructions page 138 Transcendental Instructions page 141 Constant Instructions page 143 Processor Control Instructions page 145

~~Introduction~~

Although the Intel processor supports address-size attributes of either 16 or 32 bits, the x86 assembler only supports address-size attributes of 32 bits. The operand-size is either 16 or 32 bits. An instruction that accesses 16-bit words or 32-bit longs has an operand-size attribute of either 16 or 32 bits.

~~22 x86 Assembly Language Reference Manual—November 1995 2~~

~~Notational Conventions~~

The notational conventions used in the instructions included in this chapter are described below: • The mnemonics are expressed in a regular expression-type syntax. • When a group of letters is separated from other letters by a bar (|) within square brackets or curly braces, then the group of letters between the bars or between a bar and a closing bracket or brace is considered an atomic unit.

For example, fld[lst] means fldl, flds, or fldt; fst{ls} means fst, fstl, or fsts; and fild{l|ll} means fild, fildl, or fildll. • Square brackets ([]) denote choices, but at least one is required. • Alternatives enclosed within curly braces ({}) denote that you can use one or none of them • The vertical bar separates different sufﬁxes for operators or operands. For example, the following indicates that an 8-, 16-, or 32-bit immediate value is permitted in an instruction:

~~imm[8|16|32]~~

~~• The SunOS operators are built from the Intel operators by adding sufﬁxes to them. The 80387, 80486 deals with three data types: integer, packed decimal, and real.~~

The SunOS assembler is not typed; the operator has to carry with it the type of data item it is operating on. If the operation is on an integer, the following sufﬁxes apply: none for Intel’s short(16 bits), l for Intel’s long (32 bits), and ll for Intel’s longlong(64 bits). If the operator applies to reals, then: s is short (32 bits), l is long (64 bits), and t is temporary real(80 bits). • reg[8|16|32] deﬁnes a general-purpose register, where each number indicates one of the following:

~~32: %eax, %ecx, %edx, %ebx, %esi, %edi, %ebp, %esp 16: %ax, %cx, %dx, %bx, %si, %di, %bp, %sp 8: %al, %ah, %cl, %ch, %dl, %dh, %bl, %bh~~

~~Instruction-Set Mapping 23 2~~

• imm[8|16|32|48] — an immediate value. You define immediate values using the regular expression syntax previously described (see also Expressions and Immediate Values on page 210). If there is a choice between operand sizes, the assembler will choose the smallest representation. • mem[8|16|32|48|64|80] — a memory operand; the 8, 16, 32, 48, 64, and 80 suffixes represent byte, word, long (or float), inter-segment, double, and long double memory address quantities, respectively. • creg — a control register; the control registers are: %cr0, %cr2, %cr3, or %cr4. • r/m[8|16|32] is a general-purpose register or memory operand; the operand type is determined from the suffix. They are: 8 = byte, 16 = word, and 32 = long. The registers for each operand size are the same as reg[8|16|32] above. • dreg is a debug register; the debug registers are: %db0, %db1, %db2, %db3, %db6, %db7. • sreg is a segment register. The 16-bit segment registers are: %cs, %ds, %ss, %es, %fs, and %gs. • treg is a test register. The test registers are: %tr6 and %tr7. • freg is floating-point registers %st (%st(0)), %st(1) - %st(7). • An instruction can act on zero or more operands. An operand can be any of the following: • an immediate operand (in the instruction itself) • a register (32-bit genera, segment, or status/instruction register), (16-bit word register), and (8-bit byte register). • a pointer to a memory location. • an I/O port • Instruction syntax is: operand1 → operand2

where operand1 and operand2 are operated on and the result stored in operand2. The → arrow shows the direction. The direction is opposite of that described in the Intel Corporation i486 Microprocessor Programmer’s Reference Manual.

~~24 x86 Assembly Language Reference Manual—November 1995 2~~

• disp[8|32] — the number of bits used to deﬁne the distance of a relative jump; because the assembler only supports a 32-bit address space, only 8-bit sign extended and 32-bit addresses are supported. • immPtr — an immediate pointer; when the immediate form of a long call or a long jump is used, the selector and offset are encoded as an immediate pointer. An immediate pointer consists of $imm16, $imm32 where the ﬁrst immediate value represents the segment and the second represents the offset. • cc — condition codes; the 30 condition codes are:

Table 2-1 Condition Codes a above ae above or equal b below be below or equal c carry e equal g greater ge greater than or equal to l less than le less than or equal to na not above nae not above or equal to nb not below nbe not below or equal to nc not carry ne not equal ng not greater than nge not greater than or equal to nl not less than nle not less than or equal to

~~Instruction-Set Mapping 25 2~~

~~Table 2-1 Condition Codes (Continued)~~

~~no not overﬂow np not parity ns not sign nz not zero o overﬂow p parity pe parity even po parity odd s sign z zero~~

~~References~~

This document presumes that you are familiar with the manner in which the Intel instruction sets function. For more information on speciﬁc instruction descriptions, please refer to the Intel Corporation i486 Microprocessor Programmer’s Reference Manual.

~~Segment Register Instructions~~

~~The following are the segment register instructions supported by the x86 processor.~~

~~Load Full Pointer (lds,les, lfs, lgs, and lss)~~

~~lds{wl} mem[32|48], reg[16|32] les{wl} mem[32|48], reg[16|32] lfs{wl} mem[32|48], reg[16|32] lgs{wl} mem[32|48], reg[16|32] lss{wl} mem[32|48], reg[16|32]~~

~~Operation mem[32|48] → reg[16|32]~~

~~26 x86 Assembly Language Reference Manual—November 1995 2~~

~~Description Reads a full pointer from memory and stores it in the speciﬁed segment register (DS, ES, FS, GS or SS) with a 16- or 32-bit offset value.~~

~~Example Load a 16-bit pointer from memory location 0x44444444 into the DX register:~~

~~ldsw 0x44444444, %dx~~

~~Load a 32-bit pointer from memory location 0x33333333 into the EDX register:~~

~~ldsl 0x33333333, %edx~~

~~Pop Stack into Word (pop)~~

~~pop{wl} r/m[16|32] pop{l} [%ds|%ss|%es|%fs|%gs]~~

~~Operation stack → r/m[16|32] stack → segment register~~

~~Description Replaces the previous contents of the register or memory operand with a word or long from the top of the stack.~~

~~Replaces the previous contents of the segment register operand with a long.~~

~~For a word, SP + 2; for a long, SP + 4.~~

~~Instruction-Set Mapping 27 2~~

~~Example Replace the contents of the memory location pointed to by the EDI register, plus an offset of 4, with the word from the top of the stack:~~

~~popw 4(edi)~~

~~Replace the contents of the memory location pointed to by the EAX register with the long from the top of the stack:~~

~~popl %eax~~

~~Push Word/Long onto Stack (push)~~

~~push{wl}r/m[16|32] push{wl}imm[8|16|32] push{l} [%cs|%ds|%ss|%es|%fs|%gs]~~

~~Operation r/m[16|32] → stack segment register → stack~~

~~Description For a word, SP - 2; for a long, SP - 4. Replaces the new top of stack, pointed to by SP, with the register, memory, immediate, or segment register operand.~~

~~28 x86 Assembly Language Reference Manual—November 1995 2~~

~~Example Replaces the new top of stack with the 16-bit immediate value, -126:~~

~~pushw $-126~~

~~Replaces the new top of stack with the 32-bit immediate value, 23456789:~~

~~pushl $23456789~~

~~Replaces the new top of stack with the content of the AX register:~~

~~pushw %ax~~

~~Replaces the new top of stack with the content of the EBX register:~~

~~pushl %ebx~~

~~I/O Instructions~~

~~Input from Port (in, ins)~~

~~in{bwl} imm8 in{bwl} (%dx)~~

~~ins{bwl}~~

~~Operation imm[8|16|32] → [AL|AX|EAX] DX → [AL|AX|EAX] DX → ES:(E)DI~~

~~Instruction-Set Mapping 29 2~~

~~Description in transfers a byte, word, or long from the immediate port into the byte, word, or long memory address pointed to by the AL, AX, or EAX register, respectively.~~

The second form of the in instruction transfers a byte, word, or long from a port (0 to 65535), speciﬁed in the DX register, into the byte, word, or long memory address pointed to by the AL, AX, or EAX register, respectively.

~~When an 8-bit port is speciﬁed, the upper-eight bits of the port address will be 0.~~

The ins instruction transfers a string from a port specified in the DX register to the memory byte or word pointed to by the ES:destination index. Load the desired port number into the DX register and the desired destination address into the DI or EDI index register before executing the ins instruction. After a transfer occurs, the destination-index register is automatically incremented or decremented as determined by the value of the direction flag (DF). The index register is incremented if DF = 0 (DF cleared by a cld instruction); it is decremented if DF = 1 (DF set by a std instruction). The increment or decrement count is 1 for a byte transfer, 2 for a word, and 4 for a long. Use the rep prefix with the ins instruction for a block transfer of CX bytes or words.

~~Example Transfer an immediate 8-bit port address into the AL register:~~

~~inb $0xff~~

~~Transfer a 16-bit port address, speciﬁed in the DX register, into the AX register:~~

~~inw (%dx)~~

~~Transfer a string from the port address, speciﬁed in the DX register, into the ES:destination index register:~~

~~insl~~

~~30 x86 Assembly Language Reference Manual—November 1995 2~~

~~Output from Port (out, outs)~~

~~out{bwl} imm8 out{bwl} (%dx)~~

~~outs{bwl}~~

~~Operation [AL|AX|EAX] → imm[8|16|32] [AL|AX|EAX] → DX ES:(E)DI → DX~~

~~Description Transfers a byte, word, or long from the memory address pointed to by the content of the AL, AX, or EAX register to the immediate 8-, 16-, or 32-bit port address.~~

~~The second form of the out instruction transfers a byte, word, or long from the AL, AX, or EAX registers respectively to a port (0 to 65535), speciﬁed by the DX register.~~

The outs instruction transfers a string from the memory byte or word pointed to by the ES:source index to the port addressed in the DX register. Load the desired port number into the DX register and the desired source address into the SI or ESI index register before executing the outs instruction. After a transfer occurs, the destination-index register is automatically incremented or decremented as determined by the value of the direction ﬂag (DF). The index register is incremented if DF = 0 (DF cleared by a cld instruction); it is decremented if DF = 1 (DF set by a std instruction). The increment or decrement count is 1 for a byte transfer, 2 for a word, and 4 for a long. Use the rep preﬁx with the outs instruction for a block transfer of CX bytes or words.

~~Instruction-Set Mapping 31 2~~

~~Example Transfer a word from the AX register into the 16-bit port address, 0xff:~~

~~outw $0xff~~

~~Transfer a long from the EAX register into the 32-bit port address speciﬁed by the DX register:~~

~~outl (%dx)~~

~~Transfer a string from the memory byte or word pointed to by the ES:source index to the port addressed in the DX register:~~

~~outsl~~

~~Flag Instructions~~

~~Load Flags into AH Register (lahf)~~

~~lahf~~

~~Operation SF:ZF:xx:AF:xx:PF:xx:CF → AH~~

~~Description Transfers the low byte of the ﬂags word to the AH register. The bits (lsb to msb) are: sign, zero, indeterminate, auxiliary carry, indeterminate, parity, indeterminate, and carry.~~

~~Example Transfer the ﬂags word into the AH register:~~

~~lahf~~

~~32 x86 Assembly Language Reference Manual—November 1995 2~~

~~Store AH into Flags (sahf)~~

~~sahf~~

~~Operation AH → SF:ZF:xx:AF:xx:PF:xx:CF~~

~~Description Loads ﬂags (sign, zero, indeterminate, auxiliary carry, indeterminate, parity, indeterminate, and carry) with values from the AH register.~~

~~Example Load values from the AH register into the ﬂags word:~~

~~sahf~~

~~Pop Stack into Flag (popf)~~

~~popf{wl}~~

~~Operation stack → ﬂags register~~

~~Description Pops the word or long from the top of the stack and stores the value in the ﬂags register. Stores a word in FLAGS; stores a long in EFLAGS.~~

~~Instruction-Set Mapping 33 2~~

~~Example Pops the word from the top of the stack and stores it in the ﬂags register:~~

~~popfw~~

~~Pops the long from the top of the stack and stores it in the eﬂags register:~~

~~popfl~~

~~Push Flag Register Onto Stack (pushf)~~

~~pushf{wl}~~

~~Operation ﬂags register → stack~~

~~Description For a word, SP - 2 and copies FLAGS to the new top of stack pointed to by SP. For a long, SP - 4 and copies EFLAGS to the new top of stack pointed to by SS:eSP.~~

~~Example Pushes the ﬂags register onto the top of the stack:~~

~~pushfw~~

~~Pushes the eﬂags register onto the top of the stack:~~

~~pushfl~~

~~34 x86 Assembly Language Reference Manual—November 1995 2~~

~~Complement Carry Flag (cmc)~~

~~cmc~~

~~Operation not CF → CF~~

~~Description Reverses the setting of the carry ﬂag; affects no other ﬂags.~~

~~Example Reverse the setting of the carry ﬂag:~~

~~cmc~~

~~Clear Carry Flag (clc)~~

~~clc~~

~~Operation 0 → CF~~

~~Description Sets the carry ﬂag to zero; affects no other ﬂags.~~

~~Example Clear the carry ﬂag:~~

~~clc~~

~~Instruction-Set Mapping 35 2~~

~~Set Carry Flag (stc)~~

~~stc~~

~~Operation 1 → CF~~

~~Description Sets the carry ﬂag to 1.~~

~~Example Set the carry ﬂag:~~

~~stc~~

~~Clear Interrupt Flag (cli)~~

~~cli~~

~~Operation 0 → IF~~

Description Clears the interrupt flag if the current privilege level is at least as privileged as IOPL; affects no other flags. External interrupts disabled at the end of the cli instruction or from that point on until the interrupt flag is set.

~~Example Clear the interrupt ﬂag:~~

~~cli~~

~~36 x86 Assembly Language Reference Manual—November 1995 2~~

~~Set Interrupt Flag (sti)~~

~~sti~~

~~Operation 1 → IF~~

~~Description Sets the interrupt ﬂag to 1.~~

~~Example Set the interrupt ﬂag:~~

~~sti~~

~~Clear Direction Flag (cld)~~

~~cld~~

~~Operation 0 → DF~~

~~Description Clears the direction ﬂag; affects no other ﬂags or registers. Causes all subsequent string operations to increment the index registers, (E)SI and/or (E)DI, used during the operation.~~

~~Example Clear the direction ﬂag:~~

~~cld~~

~~Instruction-Set Mapping 37 2~~

~~Set Direction Flag (std)~~

~~std~~

~~Operation 1 → DF~~

~~Description Sets the direction ﬂag to 1, causing all subsequent string operations to decrement the index registers, (E)SI and/or (E)DI, used during the operation.~~

~~Example Set the direction ﬂag:~~

~~std~~

~~Arithmetic Logical Instructions~~

~~Integer Addition (add)~~

~~add{bwl} reg[8|16|32], r/m[8|16|32] add{bwl} r/m[8|16|32], reg[8|16|32] add{bwl} imm[8|16|32], r/m[8|16|32]~~

~~Operation reg[8|16|32] + r/m[8|16|32] → r/m[8|16|32] r/m[8|16|32] + reg[8|16|32] → reg[8|16|32] imm[8|16|32] + r/m[8|16|32] → r/m[8|16|32]~~

~~38 x86 Assembly Language Reference Manual—November 1995 2~~

~~Description Integer adds operand1 to operand2 and stores the result in operand2.~~

~~When an immediate byte is added to a word or long, the immediate value is sign-extended to the size of the word or long operand.~~

~~If you wish to decimal adjust (daa) or ASCII adjust (aaa) the add result, use the form of add that stores the result in AL.~~

~~Example Integer adds the 8-bit constant, -126, to the content of the AL register:~~

~~addb $-126,%al~~

~~Integer adds the word contained in the effective address (addressed by the EDI register plus an offset of 4) to the content of the DX register:~~

~~addw 4(%edi),%dx~~

~~Integer adds the content of the EDX register to the effective address (addressed by the EDI register plus an offset of 4):~~

~~addl %edx, 4(%edi)~~

~~Integer Add With Carry (adc)~~

~~adc{bwl} reg[8|16|32], r/m[8|16|32] adc{bwl} r/m[8|16|32], reg[8|16|32] adc{bwl} imm[8|16|32], r/m[8|16|32]~~

~~Operation (reg[8|16|32] + CF) + r/m[8|16|32] → r/m[8|16|32] (r/m[8|16|32] + CF) + reg[8|16|32] → reg[8|16|32] (imm[8|16|32] + CF) + r/m[8|16|32] → r/m[8|16|32]~~

~~Instruction-Set Mapping 39 2~~

Description Integer adds operand1 and the carry ﬂag to operand2 and stores the result in operand2. adc is typically executed as part of a multi-byte or multi-word add operation. When an immediate byte is added to a word or long, the immediate value is sign-extended to the size of the word or long operand.

~~Example Integer add the 8-bit content of the effective memory address (ESI register plus an offset of 1) and the carry ﬂag to the content of the address in the CL register:~~

~~adcb 1(%esi), %cl~~

~~Integer add the 16-bit content of the effective memory address (EDI register plus an offset of 4) and the carry ﬂag to the content of the address in the DX register:~~

~~adcw 4(%edi), %dx~~

~~Integer add the 32-bit content of the address in the EDX register and the carry ﬂag to the effective memory address (EDI register plus an offset of 4):~~

~~adcl %edx, 4(%edi)~~

~~Integer Subtraction (sub)~~

~~sub{bwl} reg[8|16|32], r/m[8|16|32] sub{bwl} r/m[8|16|32], reg[8|16|32] sub{bwl} imm[8|16|32], r/m[8|16|32]~~

~~Operation r/m[8|16|32] − reg[8|16|32] → r/m[8|16|32] reg[8|16|32] − r/m[8|16|32] → reg[8|16|32] r/m[8|16|32] − imm[8|16|32] → r/m[8|16|32]~~

~~40 x86 Assembly Language Reference Manual—November 1995 2~~

Description Subtracts operand1 from operand2 and stores the result in operand2. When an immediate byte value is subtracted from a word, the immediate value is sign-extended to the size of the word operand before the subtract operation is executed.

~~If you wish to decimal adjust (das) or ASCII adjust (aas) the sub result, use the form of sub that stores the result in AL.~~

~~Example Integer subtract the 8-bit constant, -126, from the content of the effective address (addressed by the ESI register plus an offset of 1):~~

~~subb $-126, 1(%esi)~~

~~Integer subtract the 16-bit constant, 1234, from the content of the effective address (addressed by the EDI register plus an offset of 4):~~

~~subw $1234, 4(%edi)~~

~~Integer subtract the 32-bit content of the EDX register from the effective address (addressed by the EDI register plus an offset of 4):~~

~~subl %edx, 4(%edi)~~

~~Integer Subtraction With Borrow (sbb)~~

~~sbb{bwl} reg[8|16|32], r/m[8|16|32] sbb{bwl} r/m[8|16|32], reg[8|16|32] sbb{bwl} imm[8|16|32], r/m[8|16|32]~~

~~Operation r/m[8|16|32] − (reg[8|16|32] + CF) → r/m[8|16|32] reg[8|16|32] − (r/m[8|16|32] + CF) → reg[8|16|32] r/m[8|16|32] − (imm[8|16|32] + CF) → r/m[8|16|32]~~

~~Instruction-Set Mapping 41 2~~

Description Subtracts (operand1 and the carry ﬂag) from operand2 and stores the result in operand2. When an immediate byte value is subtracted from a word, the immediate value is sign-extended to the size of the word operand before the subtract operation is executed.

~~Example Integer subtract the 8-bit content of the CL register plus the carry ﬂag from the effective address (addressed by the ESI register plus an offset of 1):~~

~~sbbb %cl, 1(%esi)~~

~~Integer subtract the 16-bit constant, -126, plus the carry ﬂag from the AL register:~~

~~sbbw $-126, %al~~

~~Integer subtract the 32-bit constant, 12345678, plus the carry ﬂag from the effective address (addressed by the EDI register plus an offset of 4):~~

~~sbbl $12345678, 4(%edi)~~

~~Compare Two Operands (cmp)~~

~~cmp{bwl} reg[8|16|32], r/m[8|16|32] cmp{bwl} r/m[8|16|32], reg[8|16|32] cmp{bwl} imm[8|16|32], r/m[8|16|32]~~

~~Operation r/m[8|16|32] − reg[8|16|32] reg[8|16|32] − r/m[8|16|32] r/m[8|16|32] − imm[8|16|32]~~

~~42 x86 Assembly Language Reference Manual—November 1995 2~~

Description Subtracts operand1 from operand2, but does not store the result; only changes the ﬂags. cmp is typically executed in conjunction with conditional jumps and the setcc instruction. If an operand greater than one byte is compared to an immediate byte, the immediate byte value is ﬁrst sign- extended.

~~Example Compare the 8-bit constant, 0xff, with the content of the AL register:~~

~~cmpb $0xff, %al~~

~~Compare the 16-bit content of the DX register with the effective address (addressed by the EDI register plus an offset of 4):~~

~~cmpw %dx, 4(%edi)~~

~~Compare the 32-bit content of the effective address (addressed by the EDI register plus an offset of 4) to the EDX register:~~

~~cmpl 4(%edi), %edx~~

~~Increment by 1 (inc)~~

~~inc{bwl} r/m[8|16|32]~~

~~Operation r/m[8|16|32] + 1 → r/m[8|16|32]~~

~~Description Adds 1 to the operand and does not change the carry ﬂag. Use the add instruction with an immediate value of 1 to change the carry ﬂag,.~~

~~Instruction-Set Mapping 43 2~~

~~Example Add 1 to the contents of the byte at the effective address (addressed by the ESI register plus an offset of 1):~~

~~incb 1(%esi)~~

~~Add 1 to the 16-bit contents of the AX register:~~

~~incw %ax~~

~~Add 1 to the 32-bit contents at the effective address (addressed by the EDI register):~~

~~incl 4(%edi)~~

~~Decrease by 1 (dec)~~

~~dec{bwl}r/m[8|16|32]~~

~~Operation r/m[8|16|32] − 1 → r/m[8|16|32]~~

~~Description Subtracts 1 from the operand. Does not change the carry ﬂag. To change the carry ﬂag, use the sub instruction with an immediate value of 1.~~

~~44 x86 Assembly Language Reference Manual—November 1995 2~~

~~Example Subtract 1 from the 8-bit contents of the effective address (addressed by the ESI register plus an offset of 1):~~

~~decb 1(%esi)~~

~~Subtract 1 from the 16-bit contents of the BX register:~~

~~decw %bx~~

~~Subtract 1 from the 32-bit contents of the effective address (addressed by the EDI register plus an offset of 4):~~

~~decl 4(%edi)~~

~~Logical Comparison or Test (test)~~

~~test{bwl}reg[8|16|32], r/m[8|16|32] test{bwl}r/m[8|16|32], reg[8|16|32] test{bwl}imm[8|16|32], r/m[8|16|32]~~

~~Operation reg[8|16|32] and r/m[8|16|32] → r/m[8|16|32] r/m[8|16|32] and reg[8|16|32] → reg[8|16|32] imm[8|16|32] and r/m[8|16|32] → r/m[8|16|32]~~

Description Performs a bit-wise logical AND of the two operands. The result of a bitwise logical AND is 1 if the value of that bit in both operands is 1; otherwise, the result is 0. test discards the results and modifies the flags. The OF and CF flags are cleared; SF, ZF and PF flags are set according to the result.

~~Instruction-Set Mapping 45 2~~

~~Example Perform a logical AND of the constant, 0xff, and the 8-bit contents of the effective address (addressed by the ESI register plus an offset of 1):~~

~~testb $0xff, 1(%esi)~~

~~Perform a logical AND of the 16-bit contents of the DX register and the contents of the effective address (addressed by the EDI register plus an offset of 4):~~

~~testw %dx, 4(%edi)~~

~~Perform a logical AND of the constant, 0xffeeddcc, and the 32-bit contents of the effective address (addressed by the EDI register plus an offset of 4):~~

~~testl $0xffeeddcc, 4(%edi)~~

~~Shift (sal, shl, sar, shr)~~

sal{bwl} imm8, r/m[8|16|32] sal{bwl} %cl, r/m[8|16|32] shl{bwl} imm8, r/m[8|16|32] shl{bwl} %cl, r/m[8|16|32] sar{bwl} imm8, r/m[8|16|32] sar{bwl} %cl, r/m[8|16|32] shr{bwl} imm8, r/m[8|16|32] shr{bwl} %cl, r/m[8|16|32]

Operation shift-left r/m[8|16|32] by imm8 → r/m[8|16|32] shift-left r/m[8|16|32] by %cl → r/m[8|16|32] shift-right r/m[8|16|32] by imm8 → r/m[8|16|32] shift-right r/m[8|16|32] by %cl → r/m[8|16|32]

~~46 x86 Assembly Language Reference Manual—November 1995 2~~

Description sal (or its synonym shl) left shifts (multiplies) a byte, word, or long value for a count specified by an immediate value and stores the product in that byte, word, or long respectively. The second variation left shifts by a count value specified in the CL register. The high-order bit is shifted into the carry flag; the low-order bit is set to 0.

sar right shifts (signed divides) a byte, word, or long value for a count specified by an immediate value and stores the quotient in that byte, word, or long respectively. The second variation right shifts by a count value specified in the CL register. sar rounds toward negative infinity; the high- order bit remains unchanged.

shr right shifts (unsigned divides) a byte, word, or long value for a count speciﬁed by an immediate value and stores the quotient in that byte, word, or long respectively. The second variation divides by a count value speciﬁed in the CL register. shr sets the high-order bit to 0.

~~Example Right shift, count speciﬁed by the constant (253), the 8-bit contents of the effective address (addressed by the ESI register plus an offset of 1):~~

~~sarb $253, 1(%esi)~~

~~Right shift, count speciﬁed by the contents of the CL register, the 16-bit contents of the effective address (addressed by the EDI register plus an offset of 4):~~

~~shrw %cl, 4(%edi)~~

~~Left shift, count speciﬁed by the constant (253), the 32-bit contents of the effective address (addressed by the EDI register plus an offset of 4):~~

~~shll $253, 4(%edi)~~

~~Instruction-Set Mapping 47 2~~

~~Double Precision Shift Left (shld)~~

~~shld{wl}imm8, reg[16|32], r/m[16|32] shld{wl}%cl, reg[16|32], r/m[16|32]~~

Description shld double-precision left shifts a 16- or 32-bit register value into a word or long for the count speciﬁed by an immediate value, MODULO 32 (0 to 31). The result is stored in that particular word or long.

The second variation of shld double-precision left shifts a 16- or 32-bit register or memory value into a word or long for the count speciﬁed by register CL MODULO 32 (0 to 31).The result is stored in that particular word or long.

~~shld sets the SF, ZF, and PF ﬂags according to the value of the result; CS is set to the value of the last bit shifted out; OF and AF are undeﬁned.~~

Example Use the count speciﬁed by the constant, 253, to double-precision left shift a 16-bit register value from the DX register to the effective address (addressed by the EDI register plus an offset of 4):

~~shldw $253, %dx, 4(%edi)~~

~~Use the count speciﬁed (%CL MOD 32) by the 32-bit EDX register to double- precision left shift a 32-bit memory value at the effective address (addressed by the EDI register plus an offset of 4):~~

~~shldl %cl,%edx, 4(%edi)~~

~~48 x86 Assembly Language Reference Manual—November 1995 2~~

~~Double Precision Shift Right (shrd)~~

~~shrd{wl}imm8, reg[16|32], r/m[16|32] shrd{wl}%cl, reg[16|32], r/m[16|32]~~

Description shrd double-precision right shifts a 16- or 32-bit register value into a word or long for the count speciﬁed by an immediate value MODULO 32 (0 to 31). The result is stored in that particular word or long.

The second variation of shrd double-precision right shifts a 16- or 32-bit register or memory value into a word or long for the count speciﬁed by register CL MODULO 32 (0 to 31).The result is stored in that particular word or long.

~~shrd sets the SF, ZF, and PF ﬂags according to the value of the result; CS is set to the value of the last bit shifted out; OF and AF are undeﬁned.~~

Example Use the count speciﬁed by the constant, 253, to double-precision right shift a 16-bit register value from the DX register to the effective address (addressed by the EDI register plus an offset of 4):

~~shrdw $253, %dx, 4(%edi)~~

~~Use the count speciﬁed (%CL MOD 32) by the 32-bit EDX register to double-precision right shift a 32-bit memory value at the effective address (addressed by the EDI register plus an offset of 4)~~

~~shrdl %cl,%edx, 4(%edi)~~

~~Instruction-Set Mapping 49 2~~

~~One’s Complement Negation (not)~~

~~not{bwl} r/m[8|16|32]~~

~~Operation not r/m[8|16|32] → r/m[8|16|32]~~

~~Description Inverts each bit value of the byte, word, or long; that is, every 1 becomes a 0 and every 0 becomes a 1.~~

~~Example Invert each of the 8-bit values at the effective address (addressed by the ESI register plus an offset of 1):~~

~~notb 1(%esi)~~

~~Invert each of the 16-bit values at the effective address (addressed by the EDI register plus an offset of 4):~~

~~notw 4(%edi)~~

~~Invert each of the 32-bit values at the effective address (addressed by the EDI register plus an offset of 4):~~

~~notl 4(%edi)~~

~~Two’s Complement Negation (neg)~~

~~neg{bwl} r/m[8|16|32]~~

~~Operation two’s-complement r/m[8|16|32] → r/m[8|16|32]~~

~~50 x86 Assembly Language Reference Manual—November 1995 2~~

Description Replace the value of the byte, word, or long with its two’s complement; that is, neg subtracts the byte, word, or long value from 0, and puts the result in the byte, word, or long respectively.

~~neg sets the carry ﬂag to 1, unless initial value of the byte, word, or long is 0. In this case neg clears the carry ﬂag to 0.~~

~~Example Replace the 8-bit contents of the effective address (addressed by the ESI register plus an offset of 1) with its two’s complement:~~

~~negb 1(%esi)~~

~~Replace the 16-bit contents of the effective address (addressed by the EDI register plus an offset of 4) with its two’s complement:~~

~~negw 4(%edi)~~

~~Replace the 32-bit contents of the effective address (addressed by the EDI register plus an offset of 4) with its two’s complement:~~

~~negl 4(%edi)~~

~~Check Array Index Against Bounds (bound)~~

~~bound{wl}reg[16|32], r/m[16|32]~~

~~Operation r/m[16|32] bound reg[16|32] → CC is unchanged~~

~~Instruction-Set Mapping 51 2~~

Description Ensures that a signed array index (16- or 32-bit register) value falls within the upper and lower bounds of a block of memory. The upper and lower bounds are speciﬁed by a 16- or 32-bit register or memory value. If the signed array index value is not within the bounds, an Interrupt 5 occurs; the return EIP points to the bound instruction.

~~Example Check the 16-bit signed array index value in the AX register against the doubleword with the upper and lower bounds speciﬁed by DX:~~

~~boundw %ax, %dx~~

~~Check the 32-bit signed array index value in the EAX register against the doubleword with the upper and lower bounds speciﬁed by EDX:~~

~~boundl %eax, %edx~~

~~Logical And (and)~~

~~and{bwl} reg[8|16|32], r/m[8|16|32] and{bwl} r/m[8|16|32], reg[8|16|32] and{bwl} imm[8|16|32], r/m[8|16|32]~~

~~Operation reg[8|16|32] land r/m[8|16|32] → r/m[8|16|32] r/m[8|16|32] land reg[8|16|32] → reg[8|16|32] imm[8|16|32] land r/m[8|16|32] → r/m[8|16|32]~~

~~52 x86 Assembly Language Reference Manual—November 1995 2~~

~~Description Performs a logical AND of each bit in the values speciﬁed by the two operands and stores the result in the second operand.~~

~~Table 2-2 Logical AND~~

~~Values Result 0 LAND 0 0 0 LAND 1 0 1 LAND 0 0 1 LAND 1 1~~

~~Example Perform an 8-bit logical AND of the CL register and the contents of the effective address (addressed by the ESI register plus an offset of 1):~~

~~andb %cl, 1(%esi)~~

~~Perform a 16-bit logical AND of the constant, 0xffee, and the contents of the effective address (addressed by the AX register):~~

~~andw $0xffee, %ax~~

~~Perform a 32-bit logical AND of the contents of the effective address (addressed by the EDI register plus an offset of 4) and the EDX register:~~

~~andl 4(%edi), %edx~~

~~Instruction-Set Mapping 53 2~~

~~Logical Inclusive OR (or)~~

~~or{bwl} reg[8|16|32], r/m[8|16|32] or{bwl} r/m[8|16|32], reg[8|16|32] or{bwl} imm[8|16|32], r/m[8|16|32]~~

~~Operation reg[8|16|32] LOR r/m[8|16|32] → r/m[8|16|32] r/m[8|16|32] LOR reg[8|16|32] → reg[8|16|32] imm[8|16|32] LOR r/m[8|16|32] → r/m[8|16|32]~~

~~Description Performs a logical OR of each bit in the values speciﬁed by the two operands and stores the result in the second operand.~~

~~Table 2-3 Inclusive OR~~

~~Values Result 0 LOR 0 0 0 LOR 1 1 1 LOR 0 1 1 LOR 1 1~~

~~54 x86 Assembly Language Reference Manual—November 1995 2~~

~~Example Perform an 8-bit logical OR of the constant, 0xff, and the AL register:~~

~~orb $0xff, %al~~

~~Perform a 16-bit logical OR of the constant, 0xff83, and the contents of the effective address (addressed by the EDI register plus an offset of 4):~~

~~orw $0xff83, 4(%edi)~~

~~Perform a 32-bit logical OR of the EDX register and the contents of the effective address (addressed by the EDI register plus an offset of 4):~~

~~orl %edx, 4(%edi)~~

~~Logical Exclusive OR (xor)~~

~~xor{bwl} reg[8|16|32], r/m[8|16|32] xor{bwl} r/m[8|16|32], reg[8|16|32] xor{bwl} imm[8|16|32], r/m[8|16|32]~~

~~Operation reg[8|16|32] XOR r/m[8|16|32] → r/m[8|16|32] r/m[8|16|32] XOR reg[8|16|32] → reg[8|16|32] imm[8|16|32] XOR r/m[8|16|32] → r/m[8|16|32]~~

~~Instruction-Set Mapping 55 2~~

~~Description Performs an exclusive OR of each bit in the values speciﬁed by the two operands and stores the result in the second operand.~~

~~Table 2-4 Exclusive XOR~~

~~Values Result 0 XOR 0 0 0 XOR 1 1 1 XOR 0 1 1 XOR 1 0~~

~~Example Perform a 8-bit exclusive OR of the constant, 0xff, and the AL register:~~

~~xorb $0xff, %al~~

~~Perform a 16-bit exclusive OR of the constant, 0xff83, and the contents of the effective address (addressed by the EDI register plus an offset of 4):~~

~~xorw $0xff83, 4(%edi)~~

~~Perform a 32-bit exclusive OR of the EDX register and the contents of the effective address (addressed by the EDI register plus an offset of 4):~~

~~xorl %edx, 4(%edi)~~

~~Multiply and Divide Instructions~~

~~When the type sufﬁx is not included in a multiply or divide instruction, it defaults to a long.~~

~~56 x86 Assembly Language Reference Manual—November 1995 2~~

~~Signed Multiply (imul)~~

~~imulb r/m8 imulw r/m16 imul{l} r/m32 imul{wl}r/m[16|32], reg[16|32] imul{bwl}imm[16|32], r/m[16|32], reg[16|32]~~

~~Operation r/m8 × AL → AX r/m16 × AX → DX:AX r/m32 × EAX → EDX:EAX r/m[16|32] × reg[16|32] → reg|16|32] imm[16|32] × r/m[16|32] → reg|16|32]~~

Description The single-operand form of imul executes a signed multiply of a byte, word, or long by the contents of the AL, AX, or EAX register and stores the product in the AX, DX:AX or EDX:EAX register respectively.

~~The two-operand form of imul executes a signed multiply of a register or memory word or long by a register word or long and stores the product in that register word or long.~~

~~The three-operand form of imul executes a signed multiply of a 16- or 32- bit immediate by a register or memory word or long and stores the product in a speciﬁed register word or long.~~

~~imul clears the overﬂow and carry ﬂags under the following conditions:~~

~~Table 2-5 Clearing OF and CF ﬂags — imul~~

Instruction Form Condition for Clearing OF and CF r/m8 × AL → AX AL = sign-extend of AL to 16 bits r/m16 × AX → DX:AX AX= sign-extend of AX to 32 bits r/m32 × EAX → EDX:EAX EDX:EAX= sign-extend of EAX to 32 bits r/m[16|32] × reg[16|32] → reg|16|32] Product ﬁts exactly within reg[16|32] imm[16|32] × r/m[16|32] → reg|16|32] Product ﬁts exactly within reg[16|32]

~~Instruction-Set Mapping 57 2~~

~~Example Perform an 8-bit signed multiply of the AL register and the contents of the effective address (addressed by the ESI register plus an offset of 1):~~

~~imulb 1(%esi)~~

~~Perform a 16-bit signed multiply of the constant, -126, and the contents of the effective address (addressed by the EDI register plus an offset of 4). Store the result in the DX register:~~

~~imulw $-126, 4(%edi), %dx~~

~~Perform a 32-bit signed multiply of the constant, 12345678, and the contents of the effective address (addressed by the EDI register plus an offset of 4). Store the result in the EDX register:~~

~~imull $12345678, 4(%edi), %edx~~

~~Unsigned Multiplication of AL, AX or EAX(mul)~~

~~mul{bwl} r/m[8|16|32]~~

~~Operation r/m8 × AL → AX r/m16 × AX → DX:AX r/m32 × EAX → EDX:EAX~~

~~58 x86 Assembly Language Reference Manual—November 1995 2~~

~~Description mul executes a unsigned multiply of a byte, word, or long by the contents of the AL, AX, or EAX register and stores the product in the AX, DX:AX or EDX:EAX register respectively.~~

~~mul clears the overﬂow and carry ﬂags under the following conditions:~~

~~Table 2-6 Clearing OF and CF ﬂags — mul~~

Instruction Form Condition for Clearing OF and CF r/m8 × AL → AX clear to 0 if AH is 0; otherwise, set to 1 r/m16 × AX → DX:AX clear to 0 if DX is 0; otherwise, set to 1 r/m32 × EAX → EDX:EAX clear to 0 if EDX is 0; otherwise, set to 1

~~Example Perform an 8-bit unsigned multiply of the AL register and the contents of the effective address (addressed by the ESI register plus an offset of 1):~~

~~mulb 1(%esi)~~

~~Perform a 16-bit unsigned multiply of the AL register and the contents of the effective address (addressed by the EDI register plus an offset of 4):~~

~~mulw 4(%edi)~~

~~Perform a 32-bit unsigned multiply of the AL register and the contents of the effective address (addressed by the EDI register plus an offset of 1):~~

~~mull 1(%edi)~~

~~Instruction-Set Mapping 59 2~~

~~Unsigned Divide (div)~~

~~div{bwl} r/m[8|16|32]~~

~~Operation AX ÷ r/m8 → AL DX:AX ÷ r/m16 → AX EDX:EAX ÷ r/m32 → EAX~~

Description div executes unsigned division. div divides a 16-, 32-, or 64-bit register value (dividend) by a register or memory byte, word, or long (divisor). The quotient is stored in the AL, AX, or EAX register respectively.

~~The remainder is stored in AH, Dx, or EDX. The size of the divisor (8-, 16- or 32-bit operand) determines the particular register used as the dividend.~~

~~The OF, SF, ZF, AR, PF and CF ﬂags are undeﬁned.~~

~~60 x86 Assembly Language Reference Manual—November 1995 2~~

Example Perform an 8-bit unsigned divide of the AX register by the contents of the effective address (addressed by the ESI register plus an offset of 1) and store the quotient in the AL register, and the remainder in AH:

~~divb 1(%esi)~~

Perform a 16-bit unsigned divide of the DX:AX register by the contents of the effective address (addressed by the EDI register plus an offset of 4) and store the quotient in the AX register, and the remainder in DX:

~~divw 4(%edi)~~

Perform a 32-bit unsigned divide of the EDX:EAX register by the contents of the effective address (addressed by the EDI register plus an offset of 4) and store the quotient in the EAX register, and the remainder in EDX:

~~divl 4(%edi)~~

~~Signed Divide (idiv)~~

~~idiv{bwl}r/m[8|16|32]~~

~~Operation AX ÷ r/m8 → AL DX:AX ÷ r/m16 → AX EDX:EAX ÷ r/m32 → EAX~~

~~Instruction-Set Mapping 61 2~~

Description idiv executes signed division. idiv divides a 16-, 32-, or 64-bit register value (dividend) by a register or memory byte, word, or long (divisor). The size of the divisor (8-, 16- or 32-bit operand) determines the particular register used as the dividend, quotient, and remainder.

~~Table 2-7 idiv Register Assignment~~

~~Divisor Operand Size Dividend Quotient Remainder byte AX AL AH word DX:AX AX DX long EDX:EAX EAX EDX~~

If the resulting quotient is too large to ﬁt in the destination, or if the divisor is 0, an Interrupt 0 is generated. Non-integral quotients are truncated toward 0. The remainder has the same sign as the dividend; the absolute value of the remainder is always less than the absolute value of the divisor.

~~Example Perform a 16-bit signed divide of the DX:AX register by the contents of the effective address (addressed by the EDI register plus an offset of 4) and store the quotient in the AX register~~

~~divw 4(%edi)~~

~~Conversion Instructions~~

~~Convert Byte to Word (cbtw)~~

~~cbtw~~

~~Operation sign-extend AL → AX~~

~~62 x86 Assembly Language Reference Manual—November 1995 2~~

~~Description cbtw converts the signed byte in AL to a signed word in AX by extending the most-signiﬁcant bit (sign bit) of AL into all bits of AH.~~

~~Example~~

~~cbtw~~

~~Convert Word to Long (cwtl)~~

~~cwtl~~

~~Operation sign-extend AX → EAX~~

~~Description cwtl converts the signed word in AX to a signed long in EAX by extending the most-signiﬁcant bit (sign bit) of AX into two most-signiﬁcant bytes of EAX.~~

~~Example~~

~~cwtl~~

~~Convert Signed Word to Signed Double Word (cwtd)~~

~~cwtd~~

~~Operation sign-extend AX → DX:AX~~

~~Description cwtd converts the signed word in AX to a signed double word in DX:AX by extending the most-signiﬁcant bit (sign bit) of AX into all bits of DX.~~

~~Instruction-Set Mapping 63 2~~

~~Example~~

~~cwtd~~

~~Convert Signed Long to Signed Double Long (cltd)~~

~~cltd~~

~~Operation sign-extend EAX → EDX:EAX~~

~~Description cltd converts the signed long in EAX to a signed double long in EDX:EAX by extending the most-signiﬁcant bit (sign bit) of EAX into all bits of EDX.~~

~~Example~~

~~cltd~~

~~Decimal Arithmetic Instructions~~

~~Decimal Adjust AL after Addition (daa)~~

~~daa~~

~~Operation decimal-adjust AL → AL~~

~~Description Use daa only after executing the form of an add instruction that stores a two-BCD-digit byte result in the AL register. daa then adjusts AL to a two- digit packed decimal result.~~

~~64 x86 Assembly Language Reference Manual—November 1995 2~~

~~Example Decimal adjust the two-BCD-digit in the AL register:~~

~~daa~~

~~Decimal Adjust AL after Subtraction (das)~~

~~das~~

~~Operation decimal-adjust AL → AL~~

~~Description Use das only after executing the form of a sub instruction that stores a two- BCD-digit byte result in the AL register. das then adjusts AL to a two-digit packed decimal result.~~

~~Example Decimal adjust the two-BCD-digit in the AL register:~~

~~das~~

~~ASCII Adjust after Addition (aaa)~~

~~aaa~~

~~Operation ASCII-adjust AL → AL~~

~~Instruction-Set Mapping 65 2~~

Description You use aaa only after executing the form of an add instruction that stores a two-BCD-digit byte result in the AL register. aaa then adjusts AL to contain the correct decimal result. The top nibble of AL is set to 0. To convert AL to an ASCII result, follow the aaa instruction with:

~~or %al, 0x30~~

~~Table 2-8 shows how aaa handles a carry.~~

~~Table 2-8 Handling a Carry~~

~~Carry Action decimal carry AH + 1; CF and AF set to 1 no decimal carry AH unchanged; CF and AF cleared to 0~~

~~Example Adjust the AL register to contain the correct decimal result after an add instruction that stores a two-BCD-digit byte.~~

~~aaa~~

~~ASCII Adjust after Subtraction (aas)~~

~~aas~~

~~Operation ASCII-adjust AL → AL~~

~~66 x86 Assembly Language Reference Manual—November 1995 2~~

Description Use aas only after executing the form of an add instruction that stores a two-BCD-digit byte result in the AL register. aas then adjusts AL to contain the correct decimal result. The top nibble of AL is set to 0. To convert AL to an ASCII result, follow the aas instruction with:

~~or %al, 0x30~~

~~Table 2-9 shows how aas handles a carry.~~

~~Table 2-9 How aas Handles a Carry~~

~~Carry Action decimal carry AH - 1; CF and AF set to 1 no decimal carry AH unchanged; CF and AF cleared to 0~~

~~Example Adjust the AL register to contain the correct decimal result after a sub instruction that stores a two-BCD-digit byte~~

~~aas~~

~~ASCII Adjust AX after Multiply (aam)~~

~~aam~~

~~Operation AL ÷ 10 → AH mod 10 AL → AL~~

Description You use aam only after executing a mul instruction between two BCD digits (unpacked). mul stores the result in the AX register. The result is less than 100 so it can be contained in the AL register (the low byte of the AX

~~Instruction-Set Mapping 67 2~~

~~register). aam unpacks the AL result by dividing AL by 10, stores the quotient (most-signiﬁcant digit) in AH, and stores the remainder (least- signiﬁcant digit) in AL.~~

~~Example Adjust the AL register to contain the correct decimal result after a mul instruction between two BCD digits:~~

~~aam~~

~~ASCII Adjust AX before Division (aad)~~

~~aad~~

~~Operation AL + (AH × 10) → AL 0 → AH~~

~~Description aad prepares two unpacked BCD digits for a division operation that yields an unpacked result. The least-signiﬁcant digit is in AL; the most-signiﬁcant in AH.~~

~~aad prepares the AL and AH registers:~~

~~AL + (AH × 10) → AL 0 → AH~~

~~AX is then equal to the binary equivalent of the original unpacked two-digit BCD number.~~

~~68 x86 Assembly Language Reference Manual—November 1995 2~~

~~Example Adjust the AL and AH registers for a division operation by setting the AX register equal to the original unpacked two-digit number:~~

~~aad~~

~~Coprocessor Instructions~~

~~Wait (wait, fwait)~~

~~wait fwait~~

~~Description wait — processor suspends instruction execution until the BUSY # pin is inactive (high).~~

~~fwait — processor checks for pending unmasked numeric exceptions before proceeding.~~

~~Example Suspend instruction execution until not BUSY and check for exceptions:~~

~~wait~~

~~String Instructions~~

~~All Intel string op mnemonics default to long.~~

~~Instruction-Set Mapping 69 2~~

~~Move Data from String to String (movs)~~

~~movs{bwl} movs{bwl} m[8|16|32], reg[16|32]~~

~~Operation move {bwl} [(E)SI] → ES: (E)DI] move {bwl} DS: [(E)SI] → ES: [(E)DI]~~

Description Copies the byte, word, or long in [(E)SI] to the byte, word, or long in ES:[(E)DI}. Before executing the move instruction, load the index values into the SI source- and DI destination-index registers.

~~The destination operand must be addressable from the ES register; it cannot span segments. A source operand, however, can span segments; the default is DS.~~

After the data is moved, both the source- and destination-index registers are automatically incremented or decremented as determined by the value of the direction ﬂag (DF). The index registers are incremented if DF = 0 (DF cleared by a cld instruction); they are decremented if DF = 1 (DF set by a std instruction). The increment/decrement count is 1 for a byte move, 2 for a word, and 4 for a long.

~~For a block move of CX bytes or words, precede a movs instruction with a rep preﬁx.~~

~~Example Copy the 8-bit byte from the DS:[(E)SI] to the ES:[(E)DI] register.~~

~~movsb~~

~~70 x86 Assembly Language Reference Manual—November 1995 2~~

~~Compare String Operands (cmps)~~

~~cmps{bwl}~~

~~Operation compare DS:[(E)SI] with ES:[(E)DI]~~

Description Compares the byte, word, or long in DS:[(E)SI] with the byte, word, or long in ES:[(E)DI}. Before executing the cmps instruction, load the index values into the SI source- and DI destination-index registers.

~~cmps subtracts the operand indexed by the destination-index from the operand indexed by the source-index register.~~

After the data is compared, both the source- and destination-index registers are automatically incremented or decremented as determined by the value of the direction ﬂag (DF). The index registers are incremented if DF = 0 (DF cleared by a cld instruction); they are decremented if DF = 1 (DF set by a std instruction). The increment/decrement count is 1 for a byte move, 2 for a word, and 4 for a long.

~~For a block compare of CX or ECX bytes, words or longs, precede a cmps instruction with a repz or repnz preﬁx.~~

~~Instruction-Set Mapping 71 2~~

~~Example Compare the 8-bit byte in the DS:[(E)SI] register to the ES:[(E)DI] register.~~

~~cmpsb~~

~~Compare the 16-bit word in the DS:[(E)SI] register to the ES:[(E)DI] register.~~

~~cmpsw~~

~~Compare the 32-bit word in the DS:[(E)SI] register to the ES:[(E)DI] register.~~

~~cmpsl~~

~~Store String Data (stos)~~

~~stos{bwl}~~

~~Operation store [AL|AX|EAX] → ES:[(E)DI]~~

Description Transfers the contents of the AL, AX, or EAX register to the memory byte or word addressed in the destination register relative to the ES segment. Before executing the move instruction, load the index values into the DI destination-index register.

~~The destination operand must be addressable from the ES register; it cannot span segments.~~

~~72 x86 Assembly Language Reference Manual—November 1995 2~~

~~instruction); they are decremented if DF = 1 (DF set by a std instruction). The increment/decrement count is 1 for a byte move, 2 for a word, and 4 for a long.~~

~~For a block transfer of CX bytes, words or longs, precede a stos instruction with a rep preﬁx.~~

~~Example Transfer the contents of the AL register to the memory byte addressed in the destination register, relative to the ES segment.~~

~~stosb~~

~~Transfer the contents of the AX register to the memory word addressed in the destination register, relative to the ES segment~~

~~stosw~~

~~Transfer the contents of the EAX register to the memory double-word addressed in the destination register, relative to the ES segment~~

~~stosl~~

~~The Load String Operand (lods)~~

~~lods{bwl}~~

~~Operation load ES:[(E)DI] → [AL|AX|EAX]~~

~~Instruction-Set Mapping 73 2~~

Description Loads the memory byte or word addressed in the destination register into the AL, AX, or EAX register. Before executing the lods instruction, load the index values into the SI source-index register.

After the data is loaded, the source-index register is automatically incremented or decremented as determined by the value of the direction ﬂag (DF). The index register is incremented if DF = 0 (DF cleared by a cld instruction); it is decremented if DF = 1 (DF set by a std instruction). The increment/decrement count is 1 for a byte move, 2 for a word, and 4 for a long.

For a block transfer of CX bytes, words or longs, precede a lods instruction with a rep preﬁx; however, lods is used more typically within a loop construct where further processing of the data moved into AL, AX, or EAX is usually required.

~~Example Load the memory byte addressed in the destination register, relative to the ES segment register, into the AL register.~~

~~lodsb~~

~~Load the memory word addressed in the destination register, relative to the ES segment register, into the AX register.~~

~~lodsw~~

~~Load the memory double-word addressed in the destination register, relative to the ES segment register, into the EAX register.~~

~~lodsl~~

~~74 x86 Assembly Language Reference Manual—November 1995 2~~

~~Compare String Data (scas)~~

~~scas{bwl}~~

~~Operation compare ES:[(E)DI] with [AL|AX|EAX]~~

Description Compares the memory byte or word addressed in the destination register relative to the ES segment with the contents of the AL, AX, or EAX register. The result is discarded; only the ﬂags are set.

~~Before executing the scas instruction, load the index values into the DI destination-index register. The destination operand must be addressable from the ES register; it cannot span segments.~~

After the data is transferred, the destination-index register is automatically incremented or decremented as determined by the value of the direction ﬂag (DF). The index registers are incremented if DF = 0 (DF cleared by a cld instruction); they are decremented if DF = 1 (DF set by a std instruction). The increment/decrement count is 1 for a byte move, 2 for a word, and 4 for a long.

~~For a block search of CX or ECX bytes, words or longs, precede a scas instruction with a repz or repnz preﬁx.~~

~~Instruction-Set Mapping 75 2~~

~~Example Compare the memory byte addressed in the destination register, relative to the ES segment, with the contents of the AL register.~~

~~scasb~~

~~Compare the memory word addressed in the destination register, relative to the ES segment, with the contents of the AX register~~

~~scasw~~

~~Compare the memory byte double-word addressed in the destination register, relative to the ES segment, with the contents of the EAX register~~

~~scasl~~

~~Look-Up Translation Table (xlat)~~

~~xlat~~

~~Operation set AL to DS:[(E)BX + unsigned AL]~~

~~Description Changes the AL register from the table index to the table entry. AL should be the unsigned index into a table addressed by DS:BX (16-bit address) or DS:EBX (32-bit address).~~

~~Example Change the AL register from the table index to the table entry.~~

~~xlat~~

~~76 x86 Assembly Language Reference Manual—November 1995 2~~

~~Repeat String Operation (rep, repnz, repz)~~

~~rep repnz repz~~

~~Operation repeat string-operation until tested-condition~~

Description Use the rep (repeat while equal), repnz (repeat while nonzero) or repz (repeat while zero) prefixes in conjunction with string operations. Each prefix causes the associated string instruction to repeat until the count register (CX) or the zero flag (ZF) matches a tested condition.

~~Example Repeat while equal: Copy the 8-bit byte from the DS:[(E)SI] to the ES:[(E)DI] register.~~

~~rep movsb~~

~~Repeat while not zero: Compare the memory byte double-word addressed in the destination register EDL, relative to the ES segment, with the contents of the EAX register.~~

~~repnz scasl~~

~~Repeat while zero:Transfer the contents of the EAX register to the memory double-word addressed in the destination register EDL, relative to the ES segment.~~

~~repz stosl~~

~~Instruction-Set Mapping 77 2~~

~~Procedure Call and Return Instructions~~

~~Far Call — Procedure Call (lcall)~~

~~lcall immptr lcall *mem48~~

~~Operation far call ptr16:{16|32} far call m16:{16|32}~~

Description The lcall instruction calls intersegment (far) procedures using a full pointer. lcall causes the procedure named in the operand to be executed. When the called procedure completes, execution ﬂow resumes at the instruction following the lcall instruction (see the return instruction).

~~lcall ptr16:{16|32} uses a four-byte or six-byte operand as a long pointer to the called procedure.~~

~~lcall m16:{16|32} fetches the long pointer from the speciﬁed memory location.~~

In Real Address Mode or Virtual 8086 Mode, the long pointer provides 16 bits for the CS register and 16 or 32 bits for the EIP register. Both forms of the lcall instruction push the CS and IP or EIP registers as a return address.

~~Example Use a four-byte operand as a long pointer to the called procedure.~~

~~lcall $0xfebc, $0x12345678~~

~~Fetch a long pointer from the memory location addressed by the edx register, offset by 3.~~

~~lcall *3(%edx)~~

~~78 x86 Assembly Language Reference Manual—November 1995 2~~

~~Near Call — Procedure Call (call)~~

~~call disp32 call *r/m32~~

~~Operation near call rel{16|32} near call r/m{16|32}~~

Description The call instruction calls near procedures using a full pointer. call causes the procedure named in the operand to be executed. When the called procedure completes, execution ﬂow resumes at the instruction following the call instruction (see the return instruction).

call rel{16|32} adds a signed offset to address of the instruction following the call instruction to determine the destination; that is, the displacement is relative to the next instruction. The displacement value is stored in the EIP register. For rel16, the upper 16 bits of EIP are cleared to zero resulting in an offset value that does not exceed 16 bits.

call r/m{16|32} speciﬁes a register or memory location from which the absolute segment offset is fetched. The offset of the instruction following the call instruction is pushed onto the stack. After the procedure completes, the offset is popped by a near ret instruction within the procedure.

~~Both forms of the call instruction have no affect on the CS register.~~

~~Example Program counter minus 0x11111111.~~

~~call .-0x11111111~~

~~Add a signed offset value to the address of the next instruction.~~

~~call *4(%edi)~~

~~Instruction-Set Mapping 79 2~~

~~Return from Procedure (ret)~~

~~ret ret imm16~~

~~Operation return to caller~~

Description The ret instruction transfers control to the return address located on the stack. This address is usually placed on the stack by a call instruction. Issue the ret instruction within the called procedure to resume execution ﬂow at the instruction following the call.

The optional numeric (16- or 32-bit) parameter to ret speciﬁes the number of stack bytes or words to be released after the return address is popped from the stack. Typically, these bytes or words are used as input parameters to the called procedure.

~~For an intersegment (near) return, the address on the stack is a segment offset that is popped onto the instruction pointer. The CS register remains unchanged.~~

~~Example Transfer control to the return address located on the stack.~~

~~ret~~

~~Transfer control to the return address located on the stack. Release the next 16-bytes of parameters.~~

~~ret $-32767~~

~~80 x86 Assembly Language Reference Manual—November 1995 2~~

~~Long Return (lret)~~

~~lret lret imm16~~

~~Operation return to caller~~

Description The lret instruction transfers control to a return address located on the stack. This address is usually placed on the stack by an lcall instruction. Issue the lret instruction within the called procedure to resume execution ﬂow at the instruction following the call.

The optional numeric (16- or 32-bit) parameter to lret speciﬁes the number of stack bytes or words to be released after the return address is popped from the stack. Typically, these bytes or words are used as input parameters to the called procedure.

~~For an intersegment (far) return, the address on the stack is a long pointer. The offset is popped ﬁrst, followed by the selector.~~

In Real Mode, CS and IP are loaded directly. In Protected mode, an intersegment return causes the processor to check the descriptor addressed by the return selector. The AR byte of the descriptor must indicate a code segment of equal or lesser privilege (or greater or equal numeric value) than the current privilege level. Returns to a lesser privilege level cause the stack to be reloaded from the value saved beyond the parameter block.

~~Instruction-Set Mapping 81 2~~

~~Example Transfer control to the return address located on the stack.~~

~~lret~~

~~Transfer control to the return address located on the stack. Release the next 16-bytes of parameters.~~

~~lret $-32767~~

~~Enter/Make Stack Frame for Procedure Parameters (enter)~~

~~enter imm16, imm8~~

~~Operation make stack frame for procedure parameters~~

Description Create the stack frame required by most block-structured high-level languages. The imm16 operand speciﬁes the number of bytes of dynamic storage allocated on the stack for the routine being entered. The imm8 operand speciﬁes the lexical nesting level (0 to 31) of the routine within the high-level language source code. The nesting level determines the number of stack frame pointers copied into the new stack frame from the preceding frame.

~~Example Create a stack frame with 0xfecd bytes of dynamic storage on the stack and a nesting level of 0xff.~~

~~enter $0xfecd, $0xff~~

~~82 x86 Assembly Language Reference Manual—November 1995 2~~

~~High Level Procedure Exit (leave)~~

~~leave~~

~~Operation set (E)SP to (E)BP, then pop (E)BP~~

Description The leave instruction reverses the actions of an enter instruction. leave copies the frame pointer to the stack point and releases the stack space formerly used by a procedure for its local variables. leave pops the old frame pointer into (E)BP, thus restoring the caller’s frame. A subsequent ret nn instruction removes any arguments pushed onto the stack of the exiting procedure.

~~Example Copy the frame pointer to the stack pointer and release the stack space.~~

~~leave~~

~~Jump Instructions~~

~~Jump if ECX is Zero (jcxz)~~

~~jcxz disp8~~

~~Operation jump to disp8 if (E)CX is 0~~

~~Instruction-Set Mapping 83 2~~

~~Description The jcxz instruction tests the contents of the CX or ECX register for 0. jcxz differs from other conditional jumps that it tests the ﬂags, rather than (E)CX.~~

~~jcxz is useful at the beginning of a loop that terminates with a conditional loop instruction; such as:~~

~~loopne .-126~~

~~In this case, jcxz tests CX or ECX for 0 prior to entering the loop, thus executing 0 times:~~

~~Example~~

~~jcxz .-126 ... loopne .-126~~

~~Loop Control with CX Counter (loop, loopnz, loopz)~~

~~loop disp8~~

~~loopnz disp8 loopne disp8~~

~~loopz disp8 loope disp8~~

~~Operation decrement count; jump to disp8 if count not equal 0~~

~~decrement count; jump to disp8 if count not equal 0 and ZF = 0~~

~~decrement count; jump to disp8 if count not equal 0 and ZF = 1~~

~~84 x86 Assembly Language Reference Manual—November 1995 2~~

Description loop decrements the count register; the ﬂags register remains unchanged. Conditions are checked for by the particular form of loop you used. If the conditions match, a short jump is made to the address speciﬁed by the disp8 operand. The range of the disp8 operand, relative to the current instruction, is +127 decimal bytes to -128 decimal bytes.

loop instructions provide iteration control and combine loop index management with conditional branching. Prior to using the loop instruction, load the count register with an unsigned iteration count. Then, add the loop instruction at the end of a series of instructions to be iterated. The disp8 operand points to the beginning of the iterative loop.

~~Example Decrement the count register and when the count is not equal to zero, jump short to the disp8 location.~~

~~loopne .-126~~

~~Jump (jmp, ljmp)~~

~~jmp disp{8|16|32} jmp *r/m{16|32}~~

~~ljmpimmPtr ljmp*mem48~~

~~jcc disp{8|32}~~

~~Operation jump short or near; displacement relative to next instruction~~

~~jump far (intersegment; 4- or 6-byte immediate address~~

~~jump if condition is met; displacement relative to next instruction~~

~~Instruction-Set Mapping 85 2~~

~~Description The jmp instruction transfers execution control to a different point in the instruction stream; records no return information.~~

~~Jumps with destinations of disp[8|16|32] or r/m[16|32] are near jumps and do not require changes to the segment register value.~~

jmp rel{16|32} adds a signed offset to the address of the instruction following the jmp instruction to determine the destination; that is, the displacement is relative to the next instruction. The displacement value is stored in the EIP register. For rel16, the upper 16 bits of EIP are cleared to zero resulting in an offset value not to exceed 16 bits.

ljmp ImmPtr or *mem48 use a four- or six-byte operand as a long pointer to the destination. In Real Address Mode or Virtual 8086 mode, the long pointer provides 16 bits for the CS register and 16 or 32 bits for the EIP register. In Protected mode, both long pointer forms consult the AR (Access Rights) byte of the descriptor indexed by the selector part of the long pointer. The jmp performs one of the following control transfers depending on the value of the AR byte:

~~• A jump to a code segment at the same privilege level • A task switch~~

~~Example Jump to the relative effective address (addressed by the EDI register plus an offset of 4):~~

~~jmp *4(%edi)~~

~~Long jump, use 0xfebc for the CS register and 0x12345678 for the EIP register:~~

~~ljmp $0xfebc, $0x12345678~~

~~Jump if not equal:~~

~~jne .+10~~

~~86 x86 Assembly Language Reference Manual—November 1995 2~~

~~Interrupt Instructions~~

~~Call to Interrupt Procedure (int, into)~~

~~int 3~~

~~int imm8~~

~~into~~

~~Operation interrupt 3 — trap to debugger~~

~~interrupt numbered by immediate byte~~

~~interrupt 4 — if overﬂow ﬂag is 1~~

Description The int instruction generates a software call to an interrupt handler. The imm8 (0 to 255) operand speciﬁes an index number into the IDT (Interrupt Descriptor Table) of the interrupt routine to be called. In Protect Mode, the IDT consists of an array of 8-byte descriptors; the descriptor for the interrupt invoked must indicate an interrupt, trap, or task gate. In Real

~~Instruction-Set Mapping 87 2~~

~~Address Mode, the IDT is an array of four byte-long pointers. In Protected and Real Address Modes, the base linear address of the IDT is deﬁned by the contents of the IDTR.~~

~~The into form of the int instruction implies interrupt 4. The interrupt occurs only if the overﬂow ﬂag is set.~~

~~The ﬁrst 32 interrupts are reserved for system use. Some of these interrupts are used for internally generated exceptions.~~

The int imm8 form of the interrupt instruction behaves like a far call except that the ﬂags register is pushed onto the stack before the return address. Interrupt procedures return via the iret instruction, which pops the ﬂags and return address from the stack.

~~In Real Address Mode, the int imm8 pushes the ﬂags, CS, and the return IP onto the stack, in that order, then jumps to the long pointer indexed by the interrupt number.~~

~~Example Trap to debugger:~~

~~int $3~~

~~Trap to interrupt 0xff:~~

~~int $0xff~~

~~Trap to interrupt 4:~~

~~into~~

~~88 x86 Assembly Language Reference Manual—November 1995 2~~

~~Interrupt Return (iret)~~

~~iret~~

~~Operation return → routine~~

Description In Real Address Mode, iret pops CS, the flags register, and the instruction pointer from the stack and resumes the routine that was interrupted. In Protected Mode, the setting of the nested task flag (NT) determines the action of iret. The IOPL flag register bits are changed when CPL equals 0 and the new flag image is popped from the stack.

iret returns from an interrupt procedure without a task switch if NT equals 0. Returned code must be equally or less privileged than the interrupt routine as indicated CS selector RPL bits popped from the stack. If the returned code is less privileged, iret pops SS and the stack pointer from the stack.

iret reverses the operation of an INT or CALL that caused the task switch if NT equals 1.The task executing iret is updated and saved in its task segment. The code that follows iret is executed if the task is re-entered.

~~Example Resume the interrupted routine:~~

~~iret~~

~~Instruction-Set Mapping 89 2~~

~~Protection Model Instructions~~

~~Store Local Descriptor Table Register (sldt)~~

~~sldtr/m16~~

~~Operation LDTR → r/m[16]~~

~~Description The Local Descriptor Table Register (LDTR) is stored by sldt as indicated by the effective address operand. LDTR is stored into the two-byte register or the memory location.~~

~~sldt is not used in application programs. It is used only in operating systems.~~

~~Example Store the LDTR in the effective address (addressed by the EBX register plus and offset of 5):~~

~~sldt 5(%ebx)~~

~~Store Task Register (str)~~

~~str r/m16~~

~~Operation STR → r/m(16~~

~~Description The contents of the task register is stored by sldt as indicated by the effective address operand. STR is stored into the two-byte register or the memory location.~~

~~90 x86 Assembly Language Reference Manual—November 1995 2~~

~~Example Store str in the effective address (addressed by the EBX register plus an offset of 5):~~

~~str 5(%ebx)~~

~~Load Local Descriptor Table Register (lldt)~~

~~lldt r/m16~~

~~Operation SELECTOR → LDTR~~

Description LDTR is loaded by LLDT. The operand (word) contains a selector to a local GDT (Global Descriptor Table). The descriptor registers are not affected.The task state segment LDT ﬁeld does not change.

~~The LDTR is marked invalid if the selector operand is 0. A #GP fault is caused by all descriptor references (except LSL VERR, VERW, or LAR instructions).~~

~~LLDT is not used in application programs. It is used in operating systems.~~

~~Example Load the LLDT register from the effective address (addressed by the EBX register plus and offset of 5):~~

~~lldt 5(%ebx)~~

~~Instruction-Set Mapping 91 2~~

~~Load Task Register (ltr)~~

~~ltr r/m16~~

~~Operation r/m16 → Task Register~~

~~Description The task register is loaded by LTR from the source register or memory location speciﬁed by the operand. The loaded task state segment is tagged busy. A task switch does not occur.~~

~~Example Load the TASK register from the effective address (addressed by the EBX register plus and offset of 5):~~

~~ltr 5(%ebx)~~

~~Verify a Segment for Reading or Writing (verr, verw)~~

~~verr r/m16 verw r/m16~~

~~Operation 1 → ZF (if segment can be read or written)~~

Description VERR and VERW contains the value of a selector in the two-byte register or memory operand. VERR and VERW determine if the indicated segment can be reached in the current privilege level and whether it is readable (VERR) or writable (VERW). If the segment can be accessed, the zero flag (ZF) is set to 1, otherwise the zero flag is set to 0. For the zero flag to be set these conditions must be met:

~~• The selector denotes a descriptor; the selector is “deﬁned”.~~

~~92 x86 Assembly Language Reference Manual—November 1995 2~~

• The selector is a code or data segment; not a task statement, LDT or a gate. • For VERR, the segment must be readable, for VERW, writable. • The descriptor privilege level (DPL) can be any value for VERR. otherwise the DPL must have the same or less privilege as the current level and the DPL of the selector.

Validation is performed as if the segment were loaded into DS, ES, FS, or GS and the indicated write or read performed. The validation results are indicated by the zero ﬂag. The value of the selector cannot result in an exception.

~~Example Determine if the segment indicated by the effective address (addressed by the EBX register plus an offset of 5) can be reached in the current privilege level and whether it is readable (VERR):~~

~~verr 5(%ebx)~~

~~Store Global/Interrupt Descriptor Table Register (sgdt, sidt)~~

~~sgdt mem48 sidt mem48~~

~~Operation DTR → mem48~~

Description The contents of the descriptor table register is copied by sgdt/sidt to the six bytes of memory specified by the operand. The first word at the effective address is assigned the LIMIT field of the register. If the operand-size attribute is 32-bits:

~~• The base ﬁeld of the register is assigned to the next three bytes. • The fourth byte is written as zero.~~

~~Instruction-Set Mapping 93 2~~

~~• The last byte is undeﬁned.~~

~~If the operand-size attribute is 16-bits, the 32-bit BASEﬁeld of the register is assigned to the next four bytes.~~

~~sgdt/sldt are not used in application programs, they are used in operating systems.~~

~~Example Copy the contents of the Global Descriptor Table Register to the speciﬁed memory location:~~

~~sgdt 0x55555555~~

~~Copy the contents of the Interrupt Descriptor Table Register to the effective address (addressed by the EBX register plus an offset of 5):~~

~~sidt 5 (%ebx)~~

~~Load Global/Interrupt Descriptor Table (lgdt, lidt)~~

~~lgdt mem48 lidt mem48~~

~~Operation MEM48 → GDTR MEM48 → IDTR~~

~~Description The GDTR and IDTR are loaded with a linear base address and limit value from a six-byte operand in memory by the lgdt/lidt instructions. For a 16-bit operand:~~

~~• Load the register with a 16-bit limit and a 24-bit base.~~

~~94 x86 Assembly Language Reference Manual—November 1995 2~~

~~• The six-byte data operand high-order eight bits are not used.~~

~~For a 32-bit operand:~~

~~• Load the register with a 16-bit limit and a 32-bit base. • The six-byte data operand high-order eight bits are used as the high-order base address bits.~~

All 48-bits of the six-byte data operand are always stored into by the sgdt/sidt instructions. For a 16-bit and a 32-bit operand, the upper eight- bits are written with the high-order eight address bits. lgdt or lidt, when used with a 16-bit operand to load the register stored by sgdt or sidt, stores the upper eight-bits as zeros.

~~lgdt and lidt are not used in application programs; they are used in operation system. lgdt and lidt are the only instructions that load a linear address directly in 80386 Protected Mode.~~

~~Example Load the Global/Interrupt Descriptor Table Register from memory address 0x55555555:~~

~~lgdt 0x55555555 lidt 0x55555555~~

~~Store Machine Status Word (smsw)~~

~~smsw r/m16~~

~~Operation MSW → r/m16~~

~~Description The machine status word is stored by smsw in the two-byte register of memory location pointed to by the effective address operand.~~

~~80386 machines should use MOV ..., CR0.~~

~~Instruction-Set Mapping 95 2~~

~~Example Store the machine status word in the effective address (addressed by the EBX register plus an offset of 5):~~

~~smsw 5(%ebx)~~

~~Load Machine Status Word (lmsw)~~

~~lmsw r/m16~~

~~Operation r/m16 → MSW~~

Description The machine status word (part of CR0) is loaded by lmsw from the source operand. lmsw can be used to switch to Protected Mode if followed by an intersegment jump to clear the instruction queue. lmsw cannot switch back to Real Address Mode.

~~lmsw is not used in application programs. It is used in operating systems.~~

~~Example Load the machine status word from the contents of the effective address (addressed by the EBX register plus an offset of 5):~~

~~lmsw 5(%ebx)~~

~~Load Access Rights (lar)~~

~~lar r/m32, reg32~~

~~Operation r/m16 (masked by FF00) → r16 r/m32 (masked by 00FxFF00) → r32~~

~~96 x86 Assembly Language Reference Manual—November 1995 2~~

Description If the selector is visible at the CPL (modified by the RPL) and is a valid descriptor type, lar stores a form of the second doubleword of the descriptor for the source selector. The designated register is loaded with the double-word (high-order) of the descriptor masked by 00FxFF00, and the zero flag is set to 1. The x in 00Fx ... indicates that these four bits loaded by lar are undefined. The zero flag is cleared if the selector is invisible or of the wrong type.

The 32-bit value is stored in the 32-bit destination register if the 32-bit operand size is speciﬁed. If the 16-bit operand size is speciﬁed, the lower 16- bits of this value are stored in the 16-bit destination register.

~~For lar, all data segment descriptors and code are valid.~~

~~Example Load access rights from the contents of the effective address (addressed by the EBX register plus an offset of 5) into the EDX register:~~

~~lar 5(%ebx) %edx~~

~~Load Segment Limit (lsl)~~

~~lsl r/m32, reg32~~

~~Operation Selector rm16 (byte) → r16 Selector rm32 (byte) → r32 Selector rm16 (page) → r16 Selector rm32 (page) → r32~~

~~Instruction-Set Mapping 97 2~~

Description lsl loads a register with a segment limit (unscrambled). The descriptor type must be accepted by lsl, and the source selector must be visible at the CPL weakened by RPL. ZF is then set to 1. Otherwise, ZF is set to 0 and the destination register is unchanged.

The segment limit is loaded as a byte value. A page value limit in the descriptor is translated by lsl to a byte limit before lsl loads it in the destination register (the 20-bit limit from the descriptor is shifted left 12 and OR’d with 00000FFFH).

~~lsl stores the 32-bit granular limit in the 16-bit destination register.~~

~~For lsl, code and data segment descriptors are valid.~~

~~Example Load a segment limit from the contents of the effective address (addressed by the EBX register plus an offset of 5) into the EDX register.~~

~~lsl 5(%ebx), %edx~~

~~Clear Task-Switched (clts)~~

~~clts~~

~~Operation 0 → TS Flag in CR0~~

~~Description The task-switched ﬂag in register CR0 is cleared by clta. The TS Flag is set by the 80386 for each task switch. The TS Flag is used as follows:~~

~~• If the TS Flag is set, each execution of the ESC instruction is trapped.~~

~~98 x86 Assembly Language Reference Manual—November 1995 2~~

~~• If the TS Flag and the MP Flag are both set, execution of a Wait instruction is trapped.~~

~~If a task switch is made after an ESC instruction is started, save the processor extension context before a new ESC instruction can be run. The fault handler resets the TS Flag and saves the context.~~

~~clts is not used in application program, it is used in operating systems.~~

~~clts can only be executed at privilege level 0.~~

~~Example Clear the TS ﬂag:~~

~~clts~~

~~Adjust RPL Field of Selector (arpl)~~

~~arplr16, r/m16~~

~~Operation If RPL 1 < RPL 2, 1 → ZF~~

Description arpl has two operands. The first operand is a 16-bit word register or memory variable that contains the value of a selector. The second operand is a word register. If the RPL field of the second operand is greater than the RPL field of the first operand, ZF is set to 1 and the RPL field of the first operand is increased to match the RPL field of the second operand. Otherwise, no change is made to the first operand and the ZF is set to 0.

~~arpl is not used in application programs, it is used in operating systems.~~

~~arpl guarantees that a selector to a subroutine does not request a privilege greater than allowed. Normally, the second operand of arpl is a register that contains the CS selector value of the caller.~~

~~Instruction-Set Mapping 99 2~~

~~Example~~

~~arpl %sp, 5(%ebx)~~

~~Bit Instructions~~

~~Bit Scan Forward (bsf)~~

~~bsf{wl} r/m[16|32], reg[16|32]~~

~~Operation (r/m = 0) 0 → ZF (r/m ≠ 0) 0 → ZF~~

Description bsf scans the bits, starting at bit 0, in the doubleword operand or the second word. If the bits are all zero, ZF is cleared. Otherwise, ZF is set and the bit index of the ﬁrst set bit, found while scanning in the forward direction, is loaded into the destination register.

~~Example~~

~~bsf 4(%edi), %edx~~

~~Bit Scan Reverse (bsr)~~

~~bsr{wl} r/m[16|32], reg[16|32]~~

~~Operation (r/m = 0) 0 → ZF (r/m ≠ 0) 0 → ZF~~

~~100 x86 Assembly Language Reference Manual—November 1995 2~~

Description bsr scans the bits, starting at the most signiﬁcant bit, in the doubleword operand or the second word. If the bits are all zero, ZF is cleared. Otherwise, ZF is set and the bit index of the ﬁrst set bit found, while scanning in the reverse direction, is loaded into the destination register

~~Example~~

~~bsr 4(%edi), %edx~~

~~Bit Test (bt)~~

~~bt{wl} imm8, r/m[16|32] bt{wl} reg[16|32], r/m[16|32]~~

~~Operation BIT [LeftSRC, RightSRC] → CF~~

~~Description The bit indicated by the ﬁrst operand (base) and the second operand (offset) are saved by bt into CF (carry ﬂag).~~

~~Example~~

~~btl $253, 4(%edi) btl %edx, 4(%edi)~~

~~Instruction-Set Mapping 101 2~~

~~Bit Test And Complement (btc)~~

~~btc{wl} imm8, r/m[16|32] btc{wl} reg[16|32], r/m[16|32]~~

~~Operation BIT [LeftSRC, RightSRC] → CF NOT BIT [LeftSRC, RightSRC] → BIT[LeftSRC, RightSRC]~~

~~Description The bit indicated by the ﬁrst operand (base) and the second operand (offset) are saved by btc into CF (carry ﬂag) and complements the bit.~~

~~Example~~

~~btl $253, 4(%edi) btl %edx, 4(%edi)~~

~~Bit Test And Reset (btr)~~

~~btr{wl} imm8, r/m[16|32] btr{wl} reg[16|32], r/m[16|32]~~

~~Operation BIT[LeftSRC, RightSRC] → CF 0 → BIT[LeftSRC, RightSRC]~~

~~Description The value of the ﬁrst operand (base) and the second operand (bit offset) are saved by btr into the carry ﬂag and then it stores 0 in the bit.~~

~~Example~~

~~btrl $253, 4(%edi) btrl $edx, 4(%edi)~~

~~102 x86 Assembly Language Reference Manual—November 1995 2~~

~~Bit Test And Set (bts)~~

~~bts{wl} imm8, r/m[16|32] bts{wl} reg[16|32], r/m[16|32]~~

~~Operation BIT[LeftSRC, RightSRC] → CF 0 → BIT[LeftSRC, RightSRC]~~

~~Description The value of the ﬁrst operand (base) and the second operand (bit offset) are saved by bts into the carry ﬂag and then it stores 1 in the bit.~~

~~Example~~

~~btsl $253, 4(%edi) btsl $edx, 4(%edi)~~

~~Exchange Instructions~~

~~Compare and Exchange (cmpxchg)[486]~~

~~cmpxchg{bwl}reg[8|16|32], r/m[8|16|32]~~

~~Example~~

~~cmpxchgb %cl, 1(%esi) cmpxchgl %edx, 4(%edi)~~

~~Instruction-Set Mapping 103 2~~

~~Floating-Point Transcendental Instructions~~

~~Floating-Point Sine (fsin)~~

~~fsin~~

~~Example Replace the contents of the top of the stack with its sine.~~

~~fsin~~

~~Floating-Point Cosine (fcos)~~

~~fcos~~

~~Example Replace the contents of the top of the stack with its cos.~~

~~fcos~~

~~Floating-Point Sine and Cosine (fsincos)~~

~~fsincos~~

~~Example Replace the contents of the top of the stack with its sine and then push the cosine onto the FPU stack.~~

~~fsincos~~

~~104 x86 Assembly Language Reference Manual—November 1995 2~~

~~Floating-Point Constant Instructions~~

~~Floating-Point Load One (fld)~~

~~fld1 fld12+ fld12e fldpi fldlg2 fldln2 fldz~~

~~Example Use these constant instructions to push often-used values onto the FPU stack.~~

~~fldl 2(%ecx)~~

~~Processor Control Floating-Point Instructions~~

~~Floating-Point Load Control Word (fldcw)~~

~~fldcwr/m16~~

~~Example Load the FPU control word with the value in the speciﬁed memory address.~~

~~fldcw 2(%ecx)~~

~~Instruction-Set Mapping 105 2~~

~~Floating-Point Load Environment (fldenv)~~

~~fldenvmem~~

~~Example Reload the FPU environment from the source-operand speciﬁed memory space.~~

~~fldenv 2(%ecx)~~

~~Miscellaneous Floating-Point Instructions~~

~~Floating-Point Different Reminder (fprem)~~

~~fprem1~~

~~Example Divide stack element 0 by stack element 1 and leave the remainder in stack element 0.~~

~~fprem~~

~~Floating-Point Comparison Instructions~~

~~Floating-Point Unsigned Compare (fucom)~~

~~fucomfreg~~

~~Description:~~

~~Compare stack element 0 with stack element (i). Use condition codes:~~

~~106 x86 Assembly Language Reference Manual—November 1995 2~~

~~No compare: 111 (i) < stack 0: 000 (i) > stack 0: 001 (i) = stack 0: 100~~

~~Example Compare stack element 0 with stack element 7.~~

~~fucom %st(7)~~

~~Floating-Point Unsigned Compare And Pop (fucomp)~~

~~fucompfreg~~

~~Description~~

~~Compare stack element 0 with stack element (i). Use condition codes shown for fucom. Then pop the stack.~~

~~Example~~

~~fucomp %st(7)~~

~~Floating-Point Unsigned Compare And Pop Two (fucompp)~~

~~fucompp~~

~~Description~~

~~Compare stack element 0 with stack element (i). Use condition codes shown for fucom. Then pop the stack twice.~~

~~Instruction-Set Mapping 107 2~~

~~Example~~

~~fucompp %st(7)~~

~~Load and Move Instructions~~

~~Load Effective Address (lea)~~

~~lea{wl} r/m[16|32], reg[16|32]~~

~~Operation Addr(m) → r16 Addr(m) → r32 Truncate to 16 bits(Addr(m)) → r16 Truncate to 16 bits(Addr(m)) → r32~~

Description The offset part of the effective address is calculated by lea and stored in the speciﬁed register. The speciﬁed register determines the operand-size attribute if the instruction. The USE attribute of the segment containing the second operand determines the address-size attribute.

~~Example~~

~~leal 0x33333333, %edx~~

~~108 x86 Assembly Language Reference Manual—November 1995 2~~

~~Move (mov)~~

~~mov{bwl}imm[8|16|32], r/m[8|16|32] mov{bwl}reg[8|16|32], r/m[8|16|32] mov{bwl}r/m[8|16|32], reg[8|16|32]~~

~~Operation SRC → DEST~~

~~Description mov stores or loads the following special registers in or from a general purpose register.~~

~~• Control registers CR0, CR2, and CR3 • Debug registers DR0, DR1, DR2, DR3, DR6, and DR7 • Test registers TR6 and TR7~~

~~These instructions always use 32-bit operands.~~

~~Example~~

~~movl %cr3, %ebp movl %db7, %ebp movl %ebp, %cr3 movl %ebp, %db7 movl %tr7, %ebp movl %ebp, %tr7~~

~~Move Segment Registers (movw)~~

~~movwsreg,r/m16 movwr/m16, sreg~~

~~Operation r/m16 → Sreg Sreg → r/m16~~

~~Instruction-Set Mapping 109 2~~

Description movw copies the ﬁrst operand to the second operand, including data from a descriptor. The descriptor table entry for the selector contains the data for the register. The DS and ES registers can be loaded with a null selector without causing an exception. Use of DS or ES however, causes a #GP(0), and no memory reference occurs.

~~All interrupts are inhibited until after the execution of the next instruction, after a movw into SS. Special actions and checks result from loading a segment register under Protected Mode.~~

~~Example~~

~~movw %CS, 5(%ebx) movw %(%ebx), %CS~~

~~Move Control Registers (mov)~~

~~mov{l}creg, reg32 mov{l}reg32, creg~~

~~Operation SRC → DEST~~

~~Description This form of mov stores or loads the Control Register CR0, CR2, or CR4 to or from a general purpose register.~~

~~These instructions are always used with 32-bit operands.~~

~~Example~~

~~movl %cr3, %ebp movl %ebp, %cr3~~

~~110 x86 Assembly Language Reference Manual—November 1995 2~~

~~Move Debug Registers (mov)~~

~~mov{l}dreg, reg32 mov{l}reg32, dreg~~

~~Operation SRC → DEST~~

~~Description This form of mov stores or loads the Debug Register DR1, DR2, or DR3, DR6, and DR7 to or from a general purpose register.~~

~~These instructions are always used with 32-bit operands.~~

~~Example~~

~~movl %db7, %ebp movl %ebp, %db7~~

~~Move Test Registers (mov)~~

~~mov{l}treg, reg32 mov{l}reg32, treg~~

~~Operation SRC → DEST~~

~~Description This form of mov stores or loads the Test Register TR6 or TR7 to or from a general purpose register.~~

~~These instructions are always used with 32-bit operands.~~

~~Instruction-Set Mapping 111 2~~

~~Example~~

~~movl %tr7, %ebp movl %ebp, %tr7~~

~~Move With Sign Extend (movsx)~~

~~movsx{wl}r/m8, reg[16|32] movsxwl r/m16, reg32~~

~~Operation SignExtend(SRC) → DEST~~

Description movsx reads the contents of the register or effective address as a word or byte. movsx then sign-extends the 16- or 32-bit value to the operand-size attribute of the instruction. The result is stored in the destination register by movsx.

~~Example~~

~~movsxbl 1(%esi), %edx movsxwl 5(%ebx), %edx~~

~~Move With Zero Extend (movzb)~~

~~movzb[wl]r/m8, reg[16|32] movzwl r/m16, reg32~~

~~Operation SignExtend(SRC) → DEST~~

~~112 x86 Assembly Language Reference Manual—November 1995 2~~

Description movzx reads the contents of the register or effective address as a word or byte. movzx then sign-extends the 16- or 32-bit value to the operand-size attribute of the instruction. The result is stored in the destination register by movzx.

~~Example~~

~~Pop Instructions~~

~~Pop All General Registers (popa)~~

~~popa{wl}~~

~~Operation POP → r16 POP → r32~~

Description The eight 16-bit general registers are popped by popa. However, the SP value is not loaded into SP, It is discarded. popa restores the general registers to their values before a previous pusha was executed. DI is the ﬁrst register popped.

The eight 32-bit registers are popped by popad. However, the ESP value is not loaded into ESP, it is discarded. popad restores the general registers to their values before a previous pushad was executed. EDI is the ﬁrst register popped.

~~Example~~

~~popal~~

~~Instruction-Set Mapping 113 2~~

~~Push Instructions~~

~~Push All General Registers (pusha)~~

~~pusha{wl}~~

~~Operation SP → r16 SP → r32~~

Description The 16-bit or 32-bit general registers are saved by pusha and pushad, respectively. The stack pointer is decremented by 16 by pusha to hold the eight word values. The stack pointer is decremented by 32 by pushad to hold the eight doubleword values. The registers are pushed onto the stack in the order received; the stack bytes appear in reverse order. DI or EDI is the last stack pushed.

~~Example~~

~~pushal~~

~~Rotate Instructions~~

~~Rotate With Carry Left (rcl)~~

~~rcl{bwl}imm8, r/m[8|16|32] rcl{bwl}%cl, r/m[8|16|32]~~

~~Operation r/m high-order bit → CF CF → r/m low-order bit r/m → ShiftLeft~~

~~114 x86 Assembly Language Reference Manual—November 1995 2~~

Description The left rotate instruction shifts all bits in the register or memory operand specified. The carry flag (CF) is included in the rotation. The most significant bit is rotated to the carry flag, the carry flag is rotated to the least significant bit position, all other bits are shifted to the left. The result includes the original value of the carry flag.

The first operand value indicates how many times the rotate takes place. The value is either the contents of the CL register or an immediate number. For a single rotate, where the first operand is one, the overflow flag (OF) is defined. For all other cases, OF is undefined. After the shift, the carry flag bit is XORed with the most significant result bit.

~~Example~~

~~rclb $1, 1(%esi) rclb $253, 1(%esi) rclb %cl, 1(%esi) rcll $1, 4(%edi) rcll $253, 4(%edi) rcll %cl, 4(%edi)~~

~~Rotate With Carry Right (rcr)~~

~~rcr{bwl}imm8, r/m[8|16|32] rcr{bwl}%cl, r/m[8|16|32]~~

~~Operation r/m high-order bit → CF CF → r/m low-order bit r/m → ShiftRight~~

Description The right rotate instruction shifts all bits in the register or memory operand specified. The carry flag (CF) is included in the rotation. The least significant bit is rotated to the carry flag, the carry flag is rotated to the most significant bit position, all other bits are shifted to the right. The result includes the

~~Instruction-Set Mapping 115 2~~

~~original value of the carry ﬂag.~~

~~Example~~

~~rcrb $1, 1(%esi) rcrb $253, 1(%esi) rcrb %cl, 1(%esi) rcrl $1, 4(%edi) rcrl $253, 4(%edi) rcrl %cl, 4(%edi)~~

~~Rotate Left (rol)~~

~~rol{bwl}imm8, r/m[8|16|32] rol{bwl}%cl, r/m[8|16|32]~~

~~Operation r/m high-order bit → CF CF → r/m low-order bit r/m → ShiftLeft~~

Description The left rotate instruction shifts all bits in the register or memory operand specified. The most significant bit is rotated to the carry flag, the carry flag is rotated to the least significant bit position, all other bits are shifted to the left. The result does not include the original value of the carry flag.

~~116 x86 Assembly Language Reference Manual—November 1995 2~~

~~Example~~

~~rclb $1, 1(%esi) rclb $253, 1(%esi) rclb %cl, 1(%esi) rcll $1, 4(%edi) rcll $253, 4(%edi) rcll %cl, 4(%edi)~~

~~Rotate Right (ror)~~

~~ror{bwl}imm8, r/m[8|16|32] ror{bwl}%cl, r/m[8|16|32]~~

~~Operation r/m high-order bit → CF CF → r/m low-order bit r/m → ShiftRight~~

Description The right rotate instruction shifts all bits in the register or memory operand specified. The least significant bit is rotated to the carry flag, the carry flag is rotated to the most significant bit position, all other bits are shifted to the right. The result does not include the original value of the carry flag.

~~Instruction-Set Mapping 117 2~~

~~Example~~

~~rcrb $1, 1(%esi) rcrb $253, 1(%esi) rcrb %cl, 1(%esi) rcrl $1, 4(%edi) rcrl $253, 4(%edi) rcrl %cl, 4(%edi)~~

~~Byte Instructions~~

~~Byte Set On Condition (setcc)~~

~~setcc r/m8~~

~~Operation ConditionTrue: 1 → r/m8 ConditionFalse: 0 → rm/8~~

Description If the condition is met, setcc stores a one byte at the destination speciﬁed by the effective address. If the condition is not met, setcc stores a zero byte. Table 2-10 on page 119 lists the setcc condition options. Similar condition options are separated by commas, followed by the ﬂag condition.

~~118 x86 Assembly Language Reference Manual—November 1995 2~~

~~Table 2-10 setcc Condition List~~

Instruction (set+cc) Set Byte If: seta, setnbe greater, not equal or less than, CF=0 & ZF=0 setae, setnc, setnb equal or greater, not carry, not less than, CF=0 setb, setc, setnae less than carry, carry = 1, not equal or greater than, CF=1 setbe, setna equal or less than, not greater than carry, CF=1 or ZF=1 sete, setz equal, zero, ZF=1 setg, setnle greater, ZF=0 or SF=OF. not equal or less, ZF=1 or SF ≠ OF setge, setnl equal or greater, not less, SF = OF setl, setnge less, not equal or greater, SF ≠ OF setle, setng equal or less, not greater, ZF = 1 and SF ≠ OF setne, setnz not equal, not zero, ZF = 0 setno not overﬂow, OF = 0 setns not sign, SF=0 seto overﬂow, OF = 1 setpe, setp parity even, parity, PF = 1 setpo, setnp parity odd, not parity, PF = 0 sets sign, SF = 1

~~Example~~

~~set(cc) 1(%esi)~~

~~Instruction-Set Mapping 119 2~~

~~Byte Swap (bswap) [486]~~

~~bswapreg[16|32]~~

~~Example Convert little/big endian to big/little endian by swapping bytes.~~

~~bswap %ebx~~

~~Exchange Instructions~~

~~Exchange And Add (xadd) [486]~~

~~xadd{bwl}reg[8|16|32], r/m[8|16|32]~~

~~Example Exchange the byte contents of the ESI register with the byte register and load the sum into the ESI register.~~

~~xaddb %cl, 1(%esi)~~

~~Exchange Register / Memory With Register (xchg)~~

~~xchg{bwl}reg[8|16|32], r/m[8|16|32]~~

~~Operation DEST → temp SRC → DEST temp → SRC~~

~~120 x86 Assembly Language Reference Manual—November 1995 2~~

Description Two operands, in either order, are exchanged by xchg. During the exchange, BUS LOCK is asserted (regardless of the value of IOPL or the LOCK preﬁx) if a memory operand is part of the exchange.

~~Example~~

xchgb %cl, 1(%esi) /*exchange byte register with EA byte */ xchgl %ebp, %eax xchgl %ebx, %eax xchgl %ecx, %eax xchgl %edi, %eax xchgl %edx, %eax xchgl %edx, 4(%edi) /*exchange word register with EA word */ xchgl %esi, %eax xchgl %esp, %eax

~~Miscellaneous Instructions~~

~~Write Back and Invalidate Cache (wbinvd) [486 only]~~

~~wbinvd~~

~~Example Write back and invalidate the cache.~~

~~wbinvd~~

~~Instruction-Set Mapping 121 2~~

~~Invalidate (invd) [486 only]~~

~~invd~~

~~Example Invalidate the entire cache.~~

~~invd~~

~~Invalidate Page (invlpg) [486 only]~~

~~invlpgmem32~~

~~Example Invalidate a single entry in the translation lookaside buffer.~~

~~invlpg 5(%ebx)~~

~~LOCK Preﬁx (lock)~~

~~lock~~

~~Operation LOCK# → NEXT Instruction~~

Description The LOCK # signal is asserted during execution of the instruction following the lock preﬁx. This signal can be used in a multiprocessor system to ensure exclusive use of shared memory while LOCK # is asserted. The bts instruction is the read-modify-write sequence used to implement test-and- run.

~~122 x86 Assembly Language Reference Manual—November 1995 2~~

~~The lock prefix works only with the instructions listed here. If a lock prefix is used with any other instructions, an undefined opcode trap is generated.~~

~~bt, bts, btr, btc m, r/imm xchg r, m xchg m, r add, or, adc, sbb, and, sub, xor m, r/imm not, neg, inc, dec m~~

~~Memory ﬁeld alignment does not affect the integrity of lock.~~

~~If a different 80386 processor is concurrently executing an instruction that has a characteristic listed here, locked access is not guaranteed. The previous instruction:~~

~~• Does not follow a lock preﬁx • Is not on the previous list of acceptable instructions • A memory operand speciﬁed has a partial overlap with the destination operand.~~

~~Example~~

~~lock~~

~~No Operation (nop)~~

~~nop~~

~~Operation NO OPERATION~~

~~Description No operations are performed by nop. The xchgl %eax, %eax instruction is an alias for the nop instruction.~~

~~Instruction-Set Mapping 123 2~~

~~Example~~

~~nop~~

~~Halt (hlt)~~

~~hlt Address Prefix addr16 Data Prefix data16~~

~~Operation HLT → ENTER HALT STATE~~

Description halt puts the 80386 in a HALT state by stopping instruction execution. Execution is resumed by an nmi or an enabled interrupt. After a halt, if an interrupt is used to continue execution, the saved CS:EIP or CS:IP value points to the next instruction (after the halt).

~~The halt instruction is privileged.~~

~~Example~~

~~hlt~~

~~124 x86 Assembly Language Reference Manual—November 1995 2~~

~~Real Transfer Instructions~~

~~Load Real (fld)~~

~~fld{lst}~~

~~Operation SRC → STACK ELEMENT 0~~

~~Description The source operand is pushed onto the stack by fld. The register used before the stack top-pointer is decremented, is the register number used if the source is a register.~~

~~Example Load stack element 7 onto stack element 0.~~

~~fld %st (7)~~

~~Store Real (fst)~~

~~fst{ls}~~

~~Operation STACK ELEMENT 0 → DESTINATION~~

~~Description The current value of stack element 0 is copied to the destination. The destination can be a single- or double-real memory operand or another register.~~

~~Instruction-Set Mapping 125 2~~

~~Example Store the contents of stack element 7 onto stack element 0.~~

~~%fst (7)~~

~~Store Real and Pop (fstp)~~

~~fstp{lst}~~

~~Operation STACK ELEMENT 0 → DESTINATION THEN POP~~

Description The current value of stack element 0 is copied to the destination. The destination can be a single-, double-, or extended-real memory operand, or another register. Then pop the stack register.

~~Example Copy the contents of stack element 0 onto stack element 7 and pop stack element 0.~~

~~%fstp (7)~~

~~Exchange Registers (fxch)~~

~~fxch~~

~~Example Exchange the contents of stack element 0 and stack element 7.~~

~~fxch %st(7)~~

~~126 x86 Assembly Language Reference Manual—November 1995 2~~

~~Integer Transfer Instructions~~

~~Integer Load (fild)~~

~~fild{l|ll}~~

~~Example Convert the integer operand (signed) into extended-real and load it onto the ﬂoating-point stack.~~

~~fild 2(%eax)~~

~~Integer Store (fist)~~

~~fist{l}~~

~~Example Convert the value in stack element 0 into a signed integer and transfer the result to register ECX with an offset of 2.~~

~~fist 2(%ecx)~~

~~Integer Store and Pop (fistp)~~

~~fistp{l|ll}~~

~~Example Convert the value in stack element 0 into a signed integer and transfer the result to register ECX with an offset of 2, then pop the stack.~~

~~fistp 2(%ecx)~~

~~Instruction-Set Mapping 127 2~~

~~Packed Decimal Transfer Instructions~~

~~Packed Decimal (BCD) Load (fbld)~~

~~fbld~~

~~Example Convert the source operand (BCD) into extended-real and push it onto the ﬂoating-point stack.~~

~~fbld 2(%ecx)~~

~~Packed Decimal (BCD) Store and Pop (fbstp)~~

~~fbstp~~

~~Example Convert the value in stack element 0 to a packed decimal integer and store the result in register ECX with an offset of 2, and pop the stack.~~

~~fbstp 2(%ecx)~~

~~128 x86 Assembly Language Reference Manual—November 1995 2~~

~~Addition Instructions~~

~~Real Add (fadd)~~

~~fadd{ls}~~

~~Example Add stack element 7 to stack element 0 and return the sum to stack element 0.~~

~~fadd %st(7), %st~~

~~Real Add and Pop (faddp)~~

~~faddp~~

~~Example Add stack element 0 to stack element 7 and return the sum to stack element 7, then pop the stack.~~

~~faddp %st, %st(7)~~

~~Integer Add (fiadd)~~

~~fiadd{l}~~

~~Example Add the integer contents of register ECX to stack element 0.~~

~~fiadd 2(%ecx)~~

~~Instruction-Set Mapping 129 2~~

~~Subtraction Instructions~~

~~Subtract Real and Pop (fsub)~~

~~fsub{ls}~~

~~Example Subtract stack element 7 from stack element 0 and return the difference to stack element 0.~~

~~fsub %st(7), %st~~

~~Subtract Real (fsubp)~~

~~fsubp~~

~~Example Subtract stack element 7 from stack element 0 and return the difference to stack element 7, then pop the stack.~~

~~fsubp %st, %st(7)~~

~~Subtract Real Reversed (fsubr)~~

~~fsubr{ls}~~

~~Example Subtract stack element 0 from stack element 7 and return the difference to stack element 0.~~

~~fsubr %st(7), %st~~

~~130 x86 Assembly Language Reference Manual—November 1995 2~~

~~Subtract Real Reversed and Pop (fsubrp)~~

~~fsubrp~~

~~Example Subtract stack element 0 from stack element 7 and return the difference to stack element 7, then pop the stack.~~

~~fsubrp %st, %st(7)~~

~~Integer Subtract (fisubrp)~~

~~fisubrp~~

~~Example Subtract stack element 0 from the integer contents of register ECX (with an offset of 2) and return the difference to register ECX, then pop the stack.~~

~~fisubrp 2(%ecx)~~

~~Integer Subtract Reverse (fisubr)~~

~~fisubr{l}~~

~~Example Subtract stack element 0 from the integer contents of register ECX (with an offset of 2) and return the difference to stack element 0.~~

~~fisubr 2(%ecx)~~

~~Instruction-Set Mapping 131 2~~

~~Multiplication Instructions~~

~~Multiply Real (fmul)~~

~~fmul{ls}~~

~~Example Multiply stack element 7 by stack element 0 and return the product to stack element 0.~~

~~fmul %st(7), %st~~

~~Multiply Real and Pop (fmulp)~~

~~fmulp~~

~~Example Multiply stack element 0 by stack element 7 and return the product to stack element 7, then pop the stack.~~

~~fmulp %st, %st(7)~~

~~Integer Multiply (fimul)~~

~~fimul{l}~~

~~Example Multiply the integer contents of register ECX by stack element 0, return the product to register ECX.~~

~~fimul 2(%ecx)~~

~~132 x86 Assembly Language Reference Manual—November 1995 2~~

~~Division Instructions~~

~~Divide Real (fdiv)~~

~~fdiv{ls}~~

~~Example Divide stack element 0 by stack element 7 and return the result to stack element 0.~~

~~fdiv %st(7), %st~~

~~Divide Real and Pop (fdivp)~~

~~fdivp~~

~~Example Divide stack element 7 by stack element 0 and return the result to stack element 7, then pop the stack.~~

~~fdivp %st, %st(7)~~

~~Divide Real Reversed (fdivr)~~

~~fdivr{ls}~~

~~Example Divide stack element 0 by stack element 7 and return the result to stack element 7.~~

~~fdivr %st, %st(7)~~

~~Instruction-Set Mapping 133 2~~

~~Divide Real Reversed and Pop (fdivrp)~~

~~fdivrp~~

~~Example Divide stack element 0 by stack element 7 and return the result to stack element 7, then pop the stack.~~

~~fdivrp %st, %st(7)~~

~~Integer Divide (fidiv)~~

~~fidiv{l}~~

~~Example Divide stack element 0 by the integer contents of register ECX, with an offset of 2, and return the result to register ECX.~~

~~fidiv 2(%ecx)~~

~~Integer Divide Reversed (fidivr)~~

~~fidivr{l}~~

~~Example Divide the integer contents of register ECX, with an offset of 2, by stack element 0 and return the result to stack element 0.~~

~~fidivr 2(%ecx)~~

~~134 x86 Assembly Language Reference Manual—November 1995 2~~

~~Floating-Point Opcode Errors~~

Warning – The SunOS x86 assembler generates the wrong object code for some of the floating-point opcodes fsub, fsubr, fdiv, and fdivr when there are two floating register operands, and the second op destination is not the zeroth floating-point register. This error has been made to many versions of the USL UNIX® system and would probably cause problems if it were fixed.

~~Replace the following instructions, in column 1, with their substitutions, in column 2, for x86 platforms:~~

Table 2-11 Floating-point Opcodes fsub %st,%st(n) fsubr %st, %st(n) fsubp %st,%st(n) fsubrp %st, %st(n) fsub fsubr fsubr %st,%st(n) fsub %st, %st(n) fsubrp %st,%st(n) fsubp %st, %st(n) fsubr fsub fdiv %st,%st(n) fdivr %st,%st(n) fdivp %st,%st(n) fdivrp %st,%st(n) fdiv fdivr fdivr %st, %st(n) fdvir %st, %st(n) fdivrp %st, %st(n) fdivp %st, %st(n) fdivr fdiv

~~Instruction-Set Mapping 135 2~~

~~Miscellaneous Arithmetic Operations~~

~~Square Root (fsqrt)~~

~~fsqrt~~

~~Example Replace stack element 0 with the square root of its value.~~

~~fsqrt~~

~~Scale (fscale)~~

~~fscale~~

~~Example Add the integer value in stack element 1 to the exponent of stack element 0 (multiplication and division by powers of 2).~~

~~fscale~~

~~Partial Remainder (fprem)~~

~~fprem~~

~~Example Divide stack element 0 by stack element 1 and return the (partial) remainder to stack element 0.~~

~~fprem~~

~~136 x86 Assembly Language Reference Manual—November 1995 2~~

~~Round to Integer (frndint)~~

~~frndint~~

~~Example Round the value in stack element 0 to an integer according to the FPU control word RC ﬁeld.~~

~~frndint~~

~~Extract Exponent and Signiﬁcand (fxtract)~~

~~fxtract~~

~~Example Separate stack element 0 into its exponent and signiﬁcand and return the exponent to stack element 0, then push the signiﬁcand onto the FPU stack.~~

~~fxtract~~

~~Absolute Value (fabs)~~

~~fabs~~

~~Example Replace stack element 0 with its absolute value.~~

~~fabs~~

~~Instruction-Set Mapping 137 2~~

~~Change Sign (fchs)~~

~~fchs~~

~~Example Replace the sign of stack element 0 with the opposite sign.~~

~~fchs~~

~~Comparison Instructions~~

~~Compare Real (fcom)~~

~~fcom{ls}~~

~~Example Compare stack element 0 with stack element 7. Condition codes contain the result: No compare=111, st 0 greater than st 7=000, st 0 less than st 7=001, equal compare=100.~~

~~fcom %st(7)~~

~~138 x86 Assembly Language Reference Manual—November 1995 2~~

~~Compare Real and Pop (fcomp)~~

~~fcomp{ls}~~

~~Example Compare stack element 0 with stack element 7. Condition codes contain the result: No compare=111, st 0 greater than st 7=000, st 0 less than st 7=001, equal compare=100, then pop the stack.~~

~~fcomp %st(7)~~

~~Compare Real and Pop Twice (fcompp)~~

~~fcompp~~

Example Compare stack element 0 with stack element 1. Condition codes contain the result: No compare=111, st 0 greater than st 7=000, st 0 less than st 7=001, equal compare=100, then pop the stack twice.

~~fcompp~~

~~Integer Compare (ficom)~~

~~ficom{l}~~

Example Integer compare stack element 0 with the contents of register ECX (with an offset of 2). Condition codes contain the result: No compare=111, st 0 greater than st 7=000, st 0 less than st 7=001, equal compare=100,

~~ficom 2(%ecx)~~

~~Instruction-Set Mapping 139 2~~

~~Integer Compare and Pop (ficomp)~~

~~ficomp{l}~~

~~ficomp 2(%ecx)~~

~~Test (ftst)~~

~~ftst~~

~~Example Compare stack element 0 with the value 0.0. Condition codes contain the result: No compare=111, st 0 greater than st 7=000, st 0 less than st 7=001, equal compare=100,~~

~~ftst~~

~~Examine (fxam)~~

~~fxam~~

~~Example Report the type of object in stack element 0. FPU ﬂags C3, C2, and C0 return the type:~~

~~140 x86 Assembly Language Reference Manual—November 1995 2~~

~~Unsupported 000~~

~~NaN 001~~

~~Normal 010~~

~~Inﬁnity 011~~

~~Zero 100~~

~~Empty 101~~

~~Denormal 110~~

~~fxam~~

~~Transcendental Instructions~~

~~Partial Tangent (fptan)~~

~~fptan~~

~~Example Replace stack element 0 with its tangent and push a value of 1 onto the FPU stack.~~

~~fptan~~

~~Instruction-Set Mapping 141 2~~

~~Partial Arctangent (fpatan)~~

~~fpatan~~

~~Example Divide stack element 1 by stack element 0, compute the arctangent and return the result in radians to stack element 1, then pop the stack.~~

~~fpatan~~

~~2x - 1 (f2xm1)~~

~~f2xm1~~

~~Example Replace the contents of stack element 0 (st) with the value of (2st-1).~~

~~f2xm1~~

~~Y * log2 X (fyl2x)~~

~~fyl2x~~

~~Example Compute the logarithm (base-2) of stack element 0 and multiply the result by stack element 1 and return the result to stack element 1, then pop the stack.~~

~~fy12x~~

~~142 x86 Assembly Language Reference Manual—November 1995 2~~

~~Y * log2 (X+1) (fyl2xp1)~~

~~fyl2xp1~~

~~Example Compute the logarithm (base-2) of stack element 0 plus 1.0 and multiply the result by stack element 1 and return the result to stack element 1, then pop the stack.~~

~~fy12xpl~~

~~Constant Instructions~~

~~Load log2 E (fldl2e)~~

~~fldl2e~~

~~Example~~

~~Push log2e onto the FPU stack~~

~~fldl2e~~

~~Load log2 10 (fldl2t)~~

~~fldl2t~~

~~Example~~

~~Push log210 onto the FPU stack.~~

~~fldl2t~~

~~Instruction-Set Mapping 143 2~~

~~Load log10 2 (fldlg2)~~

~~fldlg2~~

~~Example~~

~~Push log102 onto the FPU stack.~~

~~fldlg2~~

~~Load loge 2 (fldln2)~~

~~fldln2~~

~~Example~~

~~Push log2e onto the FPU stack.~~

~~fldln2~~

~~Load pi (fldpi)~~

~~fldpi~~

~~Example Push π onto the FPU stack.~~

~~fldpi~~

~~144 x86 Assembly Language Reference Manual—November 1995 2~~

~~Load + 0 (fldz)~~

~~fldz~~

~~Example Push +0.0 onto the FPU stack.~~

~~fldz~~

~~Processor Control Instructions~~

~~Initialize Processor (finit, fnint)~~

~~finit fninit~~

~~Example~~

~~finit~~

~~No Operation (fnop)~~

~~fnop~~

~~Example~~

~~fnop~~

~~Instruction-Set Mapping 145 2~~

~~Save State (fsave, fnsave)~~

~~fsave fnsave~~

~~Example~~

~~fsave 2(%ecx)~~

~~Store Control Word (fstcw, fnstcw)~~

~~fstcw fnstcw~~

~~Example~~

~~fstcw 2(%ecx)~~

~~Store Environment (fstenv, fnstenv)~~

~~fstenv fnstenv~~

~~Example~~

~~fstenv 2(%ecx)~~

~~146 x86 Assembly Language Reference Manual—November 1995 2~~

~~Store Status Word (fstsw, fnstsw)~~

~~fstsw fnstsw~~

~~Example~~

~~fstsw %ax~~

~~Restore State (frstor)~~

~~frstor~~

~~Example~~

~~frstor 2(%ecx)~~

~~CPU Wait (fwait, wait)~~

~~fwait wait~~

~~Example~~

~~fwait~~

~~Instruction-Set Mapping 147 2~~

~~Clear Exceptions (fclex, fnclex)~~

~~fclex fnclex~~

~~Example~~

~~fclex~~

~~Decrement Stack Pointer (fdecstp)~~

~~fdecstp~~

~~Example~~

~~fdecstp~~

~~Free Registers (ffree)~~

~~ffree~~

~~Example~~

~~ffree %st(7)~~

~~148 x86 Assembly Language Reference Manual—November 1995 2~~

~~Increment Stack Pointer (fincstp)~~

~~fincstp~~

~~Example~~

~~fincstp~~

~~Example:~~

~~Instruction-Set Mapping 149 2~~

~~150 x86 Assembly Language Reference Manual—November 1995 Assembler Output 3~~

This chapter is an overview of ELF (Executable and Linking Format) for the relocatable object ﬁles produced by the assembler. The fully detailed deﬁnition of ELF appears in the System V Application Binary Interface and the Intel 386 Processor Supplement.

~~This chapter is organized as follows:~~

~~Introduction page 151 Object Files in Executable and Linking Format (ELF) page 152~~

~~Introduction~~

The main output produced by assembling an input assembly language source file is the translation of that file into an object file in (ELF). ELF files produced by the assembler are relocatable files that hold code and/or data. They are input files for the linker. The linker combines these relocatable files with other ELF object files to create an executable file or a shared object file in the next stage of program building, after translation from source files into object files.

~~The three main kinds of ELF ﬁles are relocatable, executable and shared object ﬁles.~~

The assembler can also produce ancillary output incidental to the translation process. For example, if the assembler is invoked with the -V option, it can write information to standard output and to standard error.

~~151 3~~

The assembler also creates a default output ﬁle when standard input or multiple input ﬁles are used. Ancillary output has little direct connection to the translation process, so it is not properly a subject for this manual. Information about such output appears in as(1) manual page.

Certain assembly language statements are directives to the assembler regarding the organization or content of the object ﬁle to be generated. Therefore, they have a direct effect on the translation performed by the assembler. To understand these directives, described in Chapter 2, “Instruction- Set Mapping“, it is helpful to have some working knowledge of ELF, at least for relocatable ﬁles.

~~Object Files in Executable and Linking Format (ELF)~~

~~Relocatable ELF ﬁles produced by the assembler consist of: • An ELF header • A section header table • Sections~~

The ELF header is always the first part of an ELF file. It is a structure of fixed size and format. The fields, or members, of the structure describe the nature, organization and contents of the rest of the file. The ELF header has a field that specifies the location within the file where the section header table begins.

The section header table is an array of section headers that are structures of fixed size and format. The section headers are the elements of the array, or the entries in the table. The section header table has one entry for each section in the ELF file. However, the table can also have entries (section headers) that do not correspond to any section in the file. Such entries and their array indices are reserved. The members of each section header constitute information useful to the linker about the contents of the corresponding section, if any.

All of a relocatable file’s information that does not lie within its ELF header or its section header table lies within its sections. Sections contain most of the information needed to combine relocatable files with other ELF files to produce shared object files or executable files. Sections also contain the material to be combined. For example, sections can hold: • Relocation tables • Symbol tables • String tables

~~152 x86 Assembly Language Reference Manual—November 1995 3~~

Each section in an ELF file fills a contiguous (possibly empty) sequence of that file’s bytes. Sections never overlap. However, the (set theoretic) union of a relocatable ELF header, the section header table, and all the sections can omit some of the bytes. Bytes of a relocatable file that are not in the ELF header, or in the section header table, or in any of the sections constitute the inactive space. The contents of a file’s inactive space, if any, are unspecified.

~~ELF Header~~

~~The ELF header is always located at the beginning of the ELF file. It describes the ELF file organization and contains the actual sizes of the object file control structures.~~

~~The ELF header consists of the following ﬁelds, or members, some have the value 0 for relocatable ﬁles:~~

e_ident This is a byte array consisting of the EI_NIDENT initial bytes of the ELF header, where EI_NIDENT is a name for 16. The elements of this array mark the file as an ELF object file and provide machine-independent data that can be used to decode and interpret the file’s contents.

~~e_type Identifies the object file type. A value of 1, that has the name ET_REL, specifies a relocatable file. Table 3-1 describes all the object file types.~~

~~e_machine Specifies the required architecture for an individual file. A value of 3, that has the name EM_386, specifies Intel 80386. EM_486, specifies Intel 80486.~~

~~e_version Identifies the version of this object file’s format. This field should have the current version number, named EV_CURRENT.~~

~~e_entry Virtual address where the process is to start. A value of 0 indicates no associated entry point.~~

~~Assembler Output 153 3~~

~~e_phoff Program header table’s ﬁle offset, in bytes. The value of 0 indicates no program header. (Relocatable ﬁles do not need a program header table.)~~

~~e_shoff Section header table’s ﬁle offset, in bytes. The value of 0 indicates no section header table. (Relocatable ﬁles must have a section header table.)~~

~~e_flag Processor-specific flags associated with the file. For the Intel 80386, this field has value 0.~~

~~e_ehsize ELF header’s size, in bytes.~~

~~e_phentsize Size, in bytes, of entries in the program header table. All entries are the same size. (Relocatable ﬁles do not need a program header table.)~~

~~e_phnum Number of entries in program header table. A value of 0 indicates the ﬁle has no program header table. (Relocatable ﬁles do not need a program header table.)~~

~~e_shentsize Size, in bytes, of the section header structure. A section header is one entry in the section header table; all entries are the same size.~~

~~e_shnum Number of entries in section header table. A value of 0 indicates the ﬁle has no section header table. (Relocatable ﬁles must have a section header table.)~~

~~154 x86 Assembly Language Reference Manual—November 1995 3~~

e_shstrndx Section header table index of the entry associated with the section name string table. A value of SHN_UNDEF indicates the ﬁle does not have a section name string table. Table 3-1 Object File Types

~~Type Value Description~~

~~none 0 No ﬁle type~~

~~rel 1 Relocatable ﬁle~~

~~exec 2 Executable ﬁle~~

~~dyn 3 Shared object ﬁle~~

~~core 4 Core ﬁle~~

~~loproc 0xff00 Processor-speciﬁc~~

~~hiproc 0xffff Processor-speciﬁc~~

~~Section Header~~

The section header table has all of the information necessary to locate and isolate each of the ﬁle’s sections. A section header entry in a section header table contains information characterizing the contents of the corresponding section, if the ﬁle has such a section.

~~Each entry in the section header table is a section header. A section header is a structure of ﬁxed size and format, consisting of the following ﬁelds, or members:~~

sh_name Speciﬁes the section name. The value of this ﬁeld is an index into the section header string table section, wherein it indicates the beginning of a null- terminated string that names the section.

~~sh_type Categorizes the section’s contents and semantics. Table 3-3 describes the section types.~~

~~Assembler Output 155 3~~

~~sh_flags One-bit descriptions of section attributes. Table 3-2 describes the section attribute ﬂags.~~

~~sh_addr Address where the ﬁrst byte resides if the section appears in the memory image of a process; a value of 0 indicates the section does not appear in the memory image of a process.~~

~~sh_offset Specifies the byte offset from the beginning of the file to the first byte in the section.~~

Note – If the section type is SHT_NOBITS, the corresponding section occupies no space in the file. In this case, sh_offset specifies the location at which the section would have begun if it did occupy space within the file.

~~sh_size Speciﬁes the size, in byte units, of the section.~~

~~Note – Even if the section type is SHT_NOBITS, sh_size can be nonzero; however, the corresponding section still occupies no space in the ﬁle.~~

~~sh_link Section header table index link. The interpretation of this information depends on the section type, as described in Table 3-3.~~

~~sh_info Extra information. The interpretation of this information depends on the section type, as described in Table 3-3.~~

sh_addralign If a section has an address alignment constraint, the value in this ﬁeld is the modulus, in byte units, by which the value of sh_addr must be congruent to 0; i.e., sh_addr = 0 (mod sh_addralign).

~~156 x86 Assembly Language Reference Manual—November 1995 3~~

For example, if a section contains a long (32 bits), the entire section must be ensured long alignment, so sh_addralign has the value 4. Only 0 and positive integral powers of 2 are currently allowed as values for this ﬁeld. A value of 0 or 1 indicates no address alignment constraints.

sh_entsize Size, in byte units, for entries in a section that is a table of ﬁxed-size entries, such as a symbol table. Has the value 0 if the section is not a table of ﬁxed- size entries Table 3-2 Section Attribute Flags

~~Flag Default Value Description~~

~~SHF_WRITE 0x1 Contains data that is writable during process execution.~~

~~SHF_ALLOC 0x2 Occupies memory during process execution. This attribute is off if a control section does not reside in the memory image of the object ﬁle.~~

~~SHF_EXECINSTR 0x4 Contains executable machine instructions.~~

~~SHF_MASKPROC 0xf0000000 Reserved for processor-speciﬁc semantics.~~

~~Table 3-3 Section Types~~

~~Interpretation by~~

~~Name Value Description sh_info sh_link~~

~~SHT_NULL 0 Marks section header as inactive; ﬁle has no 0 SHN_UNDEF corresponding section.~~

~~SHT_PROGBITS 1 Contains information deﬁned by the 0 SHN_UNDEF program, and in a format and with a meaning determined solely by the program.~~

SHT_SYMTAB 2 Is a complete symbol table, usually for link One greater than the The section editing. This table can also be used for symbol table index of header index of dynamic linking; however, it can contain the last local symbol. the associated many unnecessary symbols. string table. Note: Only one section of this type is allowed in a ﬁle

~~Assembler Output 157 3~~

~~Table 3-3 Section Types (Continued)~~

~~Interpretation by~~

~~Name Value Description sh_info sh_link~~

~~SHT_STRTAB 3 Is a string table. A ﬁle can have multiple 0 SHN_UNDEF string table sections.~~

SHT_RELA 4 Contains relocation entries with explicit The section header The section addends. A ﬁle can have multiple relocation index of the section to header index of sections. where the relocation the associated applies. symbol table.

~~SHT_HASH 5 Is a symbol rehash table. 0 The section Note: Only one section of this type is allowed header index of in a ﬁle the symbol table to which the hash table applies.~~

~~SHT_DYNAMIC 6 Contains dynamic linking information. 0 The section Note: Only one section of this type is allowed header index of in a ﬁle the string table used by entries in the section.~~

~~SHT_NOTE 7 Contains information that marks the ﬁle. 0 SHN_UNDEF~~

SHT_NOBITS 8 Contains information defined by the 0 SHN_UNDEF program, and in a format and with a meaning determined by the program. However, a section of this type occupies no space in the file, but the section header’s offset field specifies the location at which the section would have begun if it did occupy space within the file.

SHT_REL 9 Contains relocation entries without explicit The section header The section addends. A ﬁle can have multiple relocation index of the section to header index of sections. where the relocation the associated applies. symbol table.

~~SHT_SHLIB 10 Reserved. 0 SHN_UNDEF~~

~~158 x86 Assembly Language Reference Manual—November 1995 3~~

~~Table 3-3 Section Types (Continued)~~

~~Interpretation by~~

~~Name Value Description sh_info sh_link~~

SHT_DYNSYM 11 Is a symbol table with a minimal set of One greater than the The section symbols for dynamic linking. symbol table index of header index of Note: Only one section of this type is allowed the last local symbol. the associated in a ﬁle string table.

~~SHT_LOPROC 0x700 Lower and upper bounds of range of section 0 SHN_UNDEF SHT_HIPROC 00000 types reserved for processor-speciﬁc 0x7ffff semantics. fff~~

SHT_LOUSER 0x800 Lower and upper bounds of range of section 0 SHN_UNDEF SHT_HIUSER 00000 types reserved for application programs. 0xfffff Note: Section types in this range can be used fff by an application without conﬂicting with system-deﬁned section types.

~~Note – Some section header table indices are reserved, and the object ﬁle does not contain sections for these special indices.~~

~~Sections~~

A section is the smallest unit of an object ﬁle that can be relocated. Sections containing the following material usually appear in relocatable ELF ﬁles: • Executable text • Read-only data • Read-write data • Read-write uninitialized data (only section header appears)

Sections do not need to occur in any particular order within the object file. The sections of a relocatable ELF file contain all of the file information that is not contained in the ELF header or in the section header table. The sections in any ELF file must satisfy several conditions:

~~Assembler Output 159 3~~

1. Every section in the ﬁle must have one section header entry in the section header table to describe the section. However, the section header table can have section header entries that correspond to no section in the ﬁle.

2. Each section occupies one contiguous sequence of bytes within a ﬁle. The section can be empty (even so, its section header entry in the section header table can have a nonzero value for the ﬁeld sh_size).

~~3. A byte in a ﬁle can reside in at most one section. Sections in a ﬁle cannot overlap.~~

4. An object file can have inactive space. Inactive space is the set of all bytes in the file that are not part of the ELF header, the section header table, the program header table (for executable files), or of any section in the file. The contents of the inactive space are unspecified.

~~Sections can be added for multiple text or data segments, shared data, user- deﬁned sections, or information in the object ﬁle for debugging.~~

~~Note – Not all of the sections where there are entries in the ﬁle section header table need to be present.~~

~~Predeﬁned Sections~~

Sections having certain names beginning with "." (dot) are predefined, with their types and attributes already assigned. These special sections are of two kinds: predefined user sections and predefined nonuser sections.

~~Predeﬁned User Sections~~

Sections that an assembly language programmer can manipulate by issuing section control directives in the source file are user sections. The predefined user sections are those predefined sections that are also user sections.

~~160 x86 Assembly Language Reference Manual—November 1995 3~~

~~Table 3-4 lists the names of the predefined user sections and briefly describes each. Table 3-4 Predefined User Sections~~

~~Section Name Description~~

~~".bss" Uninitialized read-write data.~~

~~".comment" Version control information.~~

~~".data" & ".data1" Initialized read-write data.~~

~~".debug" Debugging information.~~

~~".fini" Runtime ﬁnalization instructions.~~

~~".init" Runtime initialization instructions.~~

~~".rodata" & Read-only data. ".rodata1"~~

~~".text" Executable instructions.~~

~~".line" Line # info for symbolic debugging.~~

~~".note" Special information from vendors or system builders.~~

~~Predeﬁned Non-User Sections~~

Table 3-5 shows the predefined sections that are not user sections, because assembly language programmers cannot manipulate them by issuing section control directives in the source file. Table 3-5 Predefined Non-User Sections

~~Section Name Description~~

~~".dynamic" Dynamic linking information.~~

~~".dynstr" Strings needed for dynamic linking.~~

~~".dynsym" Dynamic linking symbol table.~~

~~".got" Global offset table.~~

~~Assembler Output 161 3~~

~~Table 3-5 Predeﬁned Non-User Sections (Continued)~~

~~Section Name Description~~

~~".hash" A symbol hash table.~~

~~".interp" The path name of a program interpreter.~~

~~".plt" The procedure linking table.~~

~~"relname" & Relocation information. name is the section to which the ".relaname" relocations apply. e.g., ".rel.text", ".rela.text".~~

~~".shstrtab" String table for the section header table names.~~

~~".strtab" The string table.~~

~~".symtab" The symbol table.~~

~~Relocation Tables~~

Locations represent addresses in memory if a section is allocatable; that is, its contents are to be placed in memory at program runtime. Symbolic references to these locations must be changed to addresses by the link editor.

The assembler produces a companion relocation table for each relocatable section. The table contains a list of relocations (that is, adjustments to locations in the section) to be performed by the link editor.

~~Symbol Tables~~

The symbol table contains information to locate and relocate symbolic definitions and references. The assembler creates the symbol table section for the object file. It makes an entry in the symbol table for each symbol that is defined or referenced in the input file and is needed during linking.

~~The symbol table is then used by the link editor during relocation. The symbol table’s section header contains the symbol table index for the ﬁrst non-local symbol.~~

~~The symbol table contains the following information:~~

162 x86 Assembly Language Reference Manual—November 1995 3 st_name Index into the object file symbol string table. A value of zero indicates the corresponding entry in the symbol table has no name; otherwise, the value represents the string table index that gives the symbol name. st_value Value of the associated symbol. This value is dependent on the context; for example, it can be an address, or it can be an absolute value. st_size Size of symbol. A value of 0 indicates that the symbol has either no size or an unknown size. st_info Specifies the symbol type and binding attributes. Table 3-6 andTable 3-7 describe the symbol types and binding attributes. st_other Undefined meaning. Current value is 0. st_shndx Contains the section header table index to another relevant section, if specified. As a section moves during relocation, references to the symbol continue to point to the same location because the value of the symbol changes as well.

~~Assembler Output 163 3~~

~~Table 3-6 Symbol Types~~

~~Value Type Description~~

~~0 notype Type not speciﬁed.~~

~~1 object Symbol is associated with a data object; for example, a variable or an array.~~

2 func Symbol is associated with a function or other executable code. When another object ﬁle references a function from a shared object, the link editor automatically creates a procedure linkage table entry for the referenced symbol.

~~3 section Symbol is associated with a section. These types of symbols are primarily used for relocation.~~

~~4 file Gives the name of the source file associated with the object file.~~

~~13 loproc Values reserved for processor-speciﬁc semantics. 15 hiproc~~

~~Table 3-7 Symbol Bindings~~

~~Value Binding Description~~

~~0 local Symbol is defined in the object file and not accessible in other files. Local symbols of the same name can exist in multiple files.~~

~~1 global Symbol is either defined externally or defined in the object file and accessible in other files.~~

~~2 weak Symbol is either defined externally or defined in the object file and accessible in other files; however, these definitions have a lower precedence than globally defined symbols.~~

~~13 loproc Values reserved for processor-speciﬁc semantics. 15 hiproc~~

~~String Tables~~

A string table is a section which contains null-terminated variable-length character sequences, or strings. The object file uses these strings to represent symbol names and file names. The strings are referenced by indices into the string table section. The first and last bytes of a string table must be the null character. • A string table index can refer to any byte in the section.

~~164 x86 Assembly Language Reference Manual—November 1995 3~~

~~• Empty string table sections are permitted if zero is the value of sh_size in the section header entry for the string table in the section header table.~~

~~A string can appear multiple times and can also be referenced multiple times. References to substrings can exist, and unreferenced strings are allowed.~~

~~Assembler Output 165 3~~

~~166 x86 Assembly Language Reference Manual—November 1995 Using the Assembler Command Line A~~

~~This chapter describes how to invoke the assembler and use the command-line options.~~

~~This chapter is organized as follows:~~

~~Assembler Command Line page 167 Assembler Command Line Options page 168 Disassembling Object Code page 169~~

~~Assembler Command Line~~

~~Invoke the assembler command line as follows:~~

~~as [options] [inputfile] ...~~

~~Note – The language drivers (such as cc and f77) invoke the assembler command line with the fbe command. You can use either the as or fbe command to invoke the assembler command line.~~

~~167 A~~

The as command translates the assembly language source files, inputfile, into an executable object file, objfile. The Intel assembler recognizes the file name argument hyphen (-) as the standard input. It accepts more than one file name on the command line. The input file is the concatenation of all the specified files. If an invalid option is given or the command line contains a syntax error, the Intel assembler prints the error (including a synopsis of the command line syntax and options) to standard error output, and then terminates.

The Intel assembler supports #define macros, #include ﬁles, and symbolic substitution through use of the C preprocessor cpp. The assembler invokes the preprocessor before assembly begins if it has been speciﬁed from the command line as an option. (See the -P option.)

~~Assembler Command Line Options~~

~~-Dname -Dname=def When the -P option is in effect, these options are passed to the cpp preprocessor without interpretation by the as command; otherwise, they are ignored.~~

~~-Ipath When the -P option is in effect, this option is passed to the cpp preprocessor without interpretation by the as command; otherwise, it is ignored.~~

-m This new option runs m4 macro preprocessing on input. The m4 preprocessor is more powerful than the C preprocessor (invoked by the -P option), so it is more useful for complex preprocessing. See the SunOS 5.x Reference Manual for x86 for a detailed description of the m4 macro-processor.

-o outfile Takes the next argument as the name of the output file to be produced. By default, the .s suffix, if present, is removed from the input file and the .o suffix is appended to form the output file name.

~~168 x86 Assembly Language Reference Manual—November 1995 A~~

~~-P Run cpp, the C preprocessor, on the ﬁles being assembled. The preprocessor is run separately on each input ﬁle, not on their concatenation. The preprocessor output is passed to the assembler.~~

-Q[y|n] This new option produces the “assembler version” information in the comment section of the output object file if the y option is specified; if the n option is specified, the information is suppressed.

-s This new option places all stabs in the .stabs section. By default, stabs are placed in stabs.excl sections, that are stripped out by the static linker ld during ﬁnal execution. When the -s option is used, stabs remain in the ﬁnal executable because .stab sections are not stripped out by the static linker ld.

~~-Uname When the -P option is in effect, this option is passed to the cpp preprocessor without interpretation by the as command; otherwise, it is ignored.~~

~~-V This option writes the version information on the standard error output.~~

~~Disassembling Object Code~~

~~The dis program is the object code disassembler for ELF. It produces an assembly language listing of the object ﬁle. For detailed information about this function, see the dis(1) manual page.~~

~~Using the Assembler Command Line 169 A~~

~~170 x86 Assembly Language Reference Manual—November 1995 Index~~

A instructions, 105 floating point opcode errors, 135 addresses, 162 floating point transcendental addressing mode instructions, 104 base and index, 13 I/O instructions, 29 offset, 13 immediate values, 14 scale, 13 input format, 2 to 4 segment register, 13 instruction descriptions, 12 to 25 as command, 167 addressing modes, 13 to 14 assembler (as) instructions addition instructions, 129 addition arithmetic logical instructions, 38 to fadd(), 129 55 faddp(), 129 bit instructions, 100 to 103 byte instructions, 118 to 120 fiadd(), 129 comparison instructions, 138 to 140 arithmetic logical constant instructions, 143 to 145 adc(), 39 conversion instructions, 62 to 64 add(), 38 coprocessor instructions, 69 decimal arithmetic instructions, 64 to and(), 52 68 bound(), 51 division instructions, 133 to 134 cmp(), 42 exchange instructions, 103, 120 dec(), 44 expressions, 6, 14 flag instructions, 32 to 38 inc(), 43 floating point comparison neg(), 50 instructions, 106 to 107 not(), 50 floating point constant or(), 54

171 sal(), 46 cbtw(), 62 sar(), 46 cltd(), 64 sbb(), 41 cwtd(), 63 shl(), 46 cwtl(), 63 shld(), 48 coprocessor, 69 shr(), 46 fwait(), 69 shrd(), 49 wait(), 69 decimal arithmetic, 64 sub(), 40 aaa(), 65 test(), 45 aad(), 68 xor(), 55 arithmetic/logical, 38 aam(), 67 bit aas(), 66 bsf(), 100 daa(), 64 bsr(), 100 das(), 65 bt(), 101 division btc(), 102 fdiv(), 133 btr(), 102 fdivr(), 133 bts(), 103 fdivrp(), 134 byte fidiv(), 134 bswap(), 120 fidivr(), 134, 135 setcc(), 118 exchange comparison cmpxchg(), 103 fcom(), 138 xadd(), 120 fcomp(), 139 xchg(), 120 fcompp(), 139 flag ficom(), 139 clc(), 35 ficomp(), 140 cld(), 37 ftst(), 140 cli(), 36 fxam(), 140 cmc(), 35 constant lahf(), 32 fldl2e(), 143 popf(), 33 fldl2t(), 143 pushf(), 34 fldlg2(), 144 sahf(), 33 fldln2(), 144 stc(), 36 fldpi(), 144 std(), 38 fldz(), 145 sti(), 37 conversion, 62 floating point comparison

172 x86 Assembly Language Reference Manual—November 1995 fucom(), 106 loopz(), 84 fucomp(), 107 load and move fucompp(), 107 lea(), 108 floating point constant mov(), 109, 110, 111 fld1(), 105 movsb(), 112 fld12+(), 105 movsbwl(), 112 fld12e(), 105 movw(), 109 fldlg2(), 105 movzwl(), 112 fldln2(), 105 load full pointer fldpi(), 105 lds(), 26 fldz(), 105 les(), 26 floating point transcendental lfs(), 26 fcos(), 104 lgs(), 26 fsin(), 104 lss(), 26 fsincos(), 104 miscellaneous, 122 I/O, 29 hlt(), 124 in(), 29 invd(), 122 ins(), 29 invlp(), 122 out(), 31 lock(), 122 outs(), 31 nop(), 123 integer transfer wbinvd(), 121 fild(), 127 miscellaneous arithmetic fist(), 127 operations fistp(), 127 fabs(), 137 interrupt fchs(), 138 int(), 87 fprem(), 136 into(), 87 frndint(), 137 iret(), 89 fscale(), 136 jump fsqrt(), 136 jcc(), 85 fxtract(), 137 jcxz(), 83 miscellaneous floating point jmp(), 85 fprem1(), 106 ljmp(), 85 multiply loop(), 84 fimul(), 132 loope(), 84 fmul(), 132 loopne(), 84 fmulp(), 132 multiply and divide loopnz(), 84

173 div(), 60 fstsw(), 147 idiv(), 61 wait(), 147 imul(), 57 processor control floating point imulb(), 57 fldcw(), 105 mul(), 58 fldenv(), 106 packed decimal transfer protection model, 90 to 98 fbld(), 128 arpl(), 99 fbst(), 128 lar(), 96 pop lgdt(), 94 popa(), 113 lidt(), 94 pop stack into word lldt(), 91 pop(), 27 lmsw(), 96 procedure call, 78 lsl(), 97 procedure call and return ltr(), 92 call(), 79 sgdt(), 93 enter(), 82 sidt(), 93 lcall(), 78 sldt(), 90 leave(), 83 smsw(), 95 lret(), 81 str(), 90 ret(), 80 processor control verr(), 92 fclex(), 148 verw(), 92 fdecstp(), 148 push pusha(), 114 ffree(), 148 push stack into word fincstp(), 149 push(), 28 finit(), 145 real transfer fnclex(), 148 fld(), 125 fninit(), 145 fst(), 125 fnop(), 145 fstp(), 126 fnsave(), 146 fxch(), 126 fnstcw(), 146 return, 78 fnstenv(), 146 rotate fnstsw(), 147 rcl(), 114 frstor(), 147 rcr(), 115 fsave(), 146 rol(), 116 fstcw(), 146 ror(), 117 string, 69 to 77 fstenv(), 146

174 x86 Assembly Language Reference Manual—November 1995 cmps(), 71 overview, 10 register, 10 lods(), 73 operations, dbx pseudo, 20 movs(), 70 operations, general pseudo, 14 to 18 rep(), 77 operators, 6 repnz(), 77 other floating point instructions, 106 packed decimal transfer repz(), 77 instructions, 128 scas(), 75 pop instructions, 113 stos(), 72 procedure call and return xlat(), 76 instructions, 78 to 83 process control floating point subtraction instructions, 105 to 106 fisubr(), 131 processor control instructions, 145 to fisubrp(), 131 149 fsub(), 130 protection model instructions, 90 to 99 fsubr(), 130 push instructions, 114 fsubrp(), 131 real transfer instructions, 125 to 126 subp(), 130 rotate instructions, 114 to 117 transcendental segment register instructions, 26 to 28 f2xm1(), 142 statements assignment, 3 fptan(), 141, 142 empty, 3 fyl2x(), 142 machine operation, 3 fyl2xp1(), 143 modifying, 3 integer transfer instructions, 127 pseudo operation, 3 interrupt instructions, 87 to 89 string instructions, 69 to 77 jump instructions, 83 to 85 subtraction instructions, 130 to 131 load and move instructions, 108 to SunOS vs. Intel, mnemonics, 21 to 112 149 miscellaneous arithmetic notational coventions, 23 operations, 136 to 138 symbols, 4 miscellaneous instructions, 121 to 124 syntax rules, 7 to 10 mnemonics transcendental instructions, 141 to addition, 129 143 arithmetic, 136 types, 4 to 5 multiplication instructions, 132 values, 4 to 5 multiply and divide instructions, 56 assembler command line, 167 to 61 assembler command line options, 168 object file assembly language, 1 .comment section, 6 operands immediate, 10 C memory, 10 cc language driver, 167

175 command line options ELF section header -D, 168 sh_addr, 156 -lpath, 168 sh_addralign, 156 -m, 168 sh_entsize, 157 -o outfile, 168 sh_flags, 156 -P, 169 sh_info, 156 -Q, 169 sh_link, 156 -s, 169 sh_name, 155 -Uname, 169 sh_offset, 156 -V, 169 sh_size, 156 sh_type, 155 D ELF string table, 164 ELF symbol table, 162 default output file, 152 st_info, 163 dis program, 169 st_name, 163 disassembling object code, 169 st_other, 163 st_shndx, 163 E st_size, 163 st_value, 163 ELF header expression e_ehsize, 154 absolute, 9 e_entry, 153 relocatable, 9 e_flag, 154 e_ident, 153 e_machine, 153 F e_phentsize, 154 f77 language driver, 167 e_phnum, 154 fbe command, 167 e_phoff, 154 .file e_shentsize, 154 ,16 e_shnum, 154 e_shoff, 154 G e_shstrndx, 155 .globl,16 e_type, 153 e_version, 153 ELF section, 159 H predefined non-user section, 161 hyphen (-), 168 predefined user section, 160 I -I option, 168 instructions addition fadd(), 129 faddp(), 129

176 x86 Assembly Language Reference Manual—November 1995 fiadd(), 129 fldz(), 145 arithmetic logical conversion adc(), 39 cbtw(), 62 add(), 38 cltd(), 64 and(), 52 cwtd(), 63 bound(), 51 cwtl(), 63 cmp(), 42 coprocessor dec(), 44 fwait(), 69 inc(), 43 wait(), 69 neg(), 50 decimal arithmetic not(), 50 aaa(), 65 or(), 54 aad(), 68 sal(), 46 aam(), 67 sar(), 46 aas(), 66 sbb(), 41 daa(), 64 shl(), 46 das(), 65 shld(), 48 division shr(), 46 fdiv(), 133 shrd(), 49 fdivr(), 133 sub(), 40 fdivrp(), 134 test(), 45 fidiv(), 134 xor(), 55 fidivr(), 134, 135 bit exchange bsf(), 100 cmpxchg(), 103 bsr(), 100 xadd(), 120 bt(), 101 xchg(), 120 btc(), 102 flag btr(), 102 clc(), 35 bts(), 103 cld(), 37 byte cli(), 36 bswap(), 120 cmc(), 35 setcc(), 118 lahf(), 32 comparison popf(), 33 fcom(), 138 pushf(), 34 fcomp(), 139 sahf(), 33 fcompp(), 139 stc(), 36 ficom(), 139 std(), 38 ficomp(), 140 sti(), 37 ftst(), 140 floating point comparison fxam(), 140 fucom(), 106 constant fucomp(), 107 fldl2e(), 143 fucompp(), 107 fldl2t(), 143 floating point constant fldlg2(), 144 fld1(), 105 fldln2(), 144 fld12+(), 105 fldpi(), 144 fld12e(), 105

177 fldlg2(), 105 invd(), 122 fldln2(), 105 invlp(), 122 fldpi(), 105 lock(), 122 fldz(), 105 nop(), 123 floating point transcendental wbinvd(), 121 fcos(), 104 miscellaneous arithmetic operations fsin(), 104 fabs(), 137 fsincos(), 104 fchs(), 138 I/O fprem(), 136 in(), 29 frndint(), 137 ins(), 29 fscale(), 136 out(), 31 fsqrt(), 136 outs(), 31 fxtract(), 137 integer transfer miscellaneous floating point fild(), 127 fprem1(), 106 fist(), 127 multiply fistp(), 127 fimul(), 132 interrupt fmul(), 132 int(), 87 fmulp(), 132 into(), 87 multiply and divide iret(), 89 div(), 60 jump idiv(), 61 jcc(), 85 imul(), 57 jcxz(), 83 imulb(), 57 jmp(), 85 mul(), 58 ljmp(), 85 packed decimal transfer loop(), 84 fbld(), 128 loope(), 84 fbst(), 128 loopne(), 84 pop loopnz(), 84 popa(), 113 loopz(), 84 pop stack into word load and move pop(), 27 lea(), 108 procedure call and return mov(), 109, 110, 111 call(), 79 movsb(), 112 enter(), 82 movsbwl(), 112 lcall(), 78 movw(), 109 leave(), 83 movzwl(), 112 lret(), 81 load full pointer ret(), 80 lds(), 26 processor control les(), 26 fclex(), 148 lfs(), 26 fdecstp(), 148 lgs(), 26 ffree(), 148 lss(), 26 fincstp(), 149 miscellaneous finit(), 145 hlt(), 124 fnclex(), 148

178 x86 Assembly Language Reference Manual—November 1995 fninit(), 145 cmps(), 71 fnop(), 145 lods(), 73 fnsave(), 146 movs(), 70 fnstcw(), 146 rep(), 77 fnstenv(), 146 repnz(), 77 fnstsw(), 147 repz(), 77 frstor(), 147 scas(), 75 fsave(), 146 stos(), 72 fstcw(), 146 xlat(), 76 fstenv(), 146 subtraction fstsw(), 147 fisubr(), 131 wait(), 147 fisubrp(), 131 processor control floating point fsub(), 130 fldcw(), 105 fsubr(), 130 fldenv(), 106 fsubrp(), 131 protection model subp(), 130 arpl(), 99 transcendental lar(), 96 f2xm1(), 142 lgdt(), 94 fptan(), 141, 142 lidt(), 94 fyl2x(), 142 lldt(), 91 fyl2xp1(), 143 lmsw(), 96 invoking, as command, 167 lsl(), 97 ltr(), 92 sgdt(), 93 L sidt(), 93 language drivers, 167 sldt(), 90 .local,17 smsw(), 95 str(), 90 verr(), 92 M verw(), 92 -m option, 168 push machine instruction syntax, 10 pusha(), 114 derived type information, 10 push stack into word destination operand, 10 push(), 28 register name, 10 real transfer source operand, 10 fld(), 125 multiple files, on as command line, 168 fst(), 125 multiple sections, 160 fstp(), 126 multiple strings, in string table, 165 fxch(), 126 rotate rcl(), 114 N rcr(), 115 .nonvolatile,17 rol(), 116 ror(), 117 string

179 notational conventions S condition codes, 25 -s option, 169 control register, 24 .section distance of relative jump, 25 ,17 immediate pointer, 25 section header, 155 immediate value, 24 sections, 159 memory operand, 24 statements append comment, 3, ?? to 4 O assignment, 3 empty, 3 operands label prefix, 3 byte register, 11 machine operation, 3 long register, 12 pseudo operation, 3 segment register, 12 string tables, 164 word register, 11 strings operations, general pseudo, 14 multiple references in string .align val ,14 table, 165 .bcd val ,15 unreferenced in string table, 165 .bss,15 strings, multiple in string table, 165 .bss tag, bytes,15 .byte val,15 sub-strings in string table .comm name, expr,15 references to, 165 .data,15 symbol, 19 .double val,15 symbol tables, 162 .even,15 symbol types options absolute, 5 command line, 168 attribute, 5 bss, 5 data, 5 P object file sections, 6 -P option, 169 text, 5 predefined non-user sections, 161 undefined, 5 predefined user sections, 160 symbol, reserved Programming Utilities - SunOS 5.0, xviii .bss, 4 pseudo-operations, 14 .data, 4 .fini, 5 .init, 5 Q .text, 4 -Q option, 169 U R -U option, 169 relocatable files, 151 relocation tables, 162 V -V option, 169

~~180 x86 Assembly Language Reference Manual—November 1995 .volatile,18~~

~~W .weak,18~~

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